Disclaimer: this turned out quite long. I'm not a blowhard, but I do have some experience with this topic. If you want a general overview of AV products (as I see them, of course), give this a read. If not, feel free to skip it and I won't be at all offended.
Hello. I've put some time into this exact question, so maybe I can share a few insights. First, make sure you don't compare apples to oranges. Norton is an antivirus product with a firewall included (albeit a very basic one). Many other antivirus scanners DO include firewalls, but others do not. It is not a measure of quality, but merely of program specification. The BEST option is often to use a separate firewall product anyway, because the ones that are included with basic antivirus programs are not always the most robust.
Norton has a good scanning engine and a good interface, but it's not a particularly well-designed program. It's huge, it installs way too many little components, it causes way too many problems on way too many computers, it slows down many computers, Symantec's support is bad, etc. It may work for you, and if it does and you don't need your computer running at peak performance or don't plan to install programs in the future that might conflict, then don't worry too much about it. You may encounter a problem at some point, and when you do you may find it hard to get answers from Symantec AND hard to uninstall the product, but then again you may never have problems. Just be aware that due to the intrusive, inelegant way the program is designed, you are more likely to encounter problems with Norton than with many other products on the market. However, as I said Norton does have a quality scanning engine.
Norton's best-known competitors at the moment are McAfee and PC-cillin. McAfee suffers from some of the same problems as Norton, in that it's a pretty bloated product. But it has fewer such quirks, and also has decent scanning and a pretty good interface. PC-cillin is the fastest and most stable of the three, and also has a few cutting-edge features that the other two don't have, like protection for wireless. PC-cillin has been gaining in popularity over the last few years partly because of the problems many people have had with Norton and McAfee (particularly over that period of time). McAfee and PC-cillin are an apples to apples comparison because they both have basic firewalls included.
There are some other competitors that are slightly less well-known but also high quality and picking up momentum. Panda has made a big splash on the scene with a program with a colorful interface and a fast, accurate scanner. I would recommend it over Norton but it may have a few quirks of its own. BitDefender is another solid all-around option that people like; it also has a quality scanning engine and no major disadvantages. Its system scan is not the fastest, though is competitive with Norton and McAfee, but its background program does not slow down a system like Norton and McAfee can. Kaspersky is a solid option. It has top-notch scanning and an interface that has improved a lot recently; it has a reputation for being better suited to power users because of its eccentricities, and this may be true to a degree but Kaspersky has improved a lot in this area. F-Secure is another option with VERY reliable scanning based on two scanning engines (including Kaspersky's). It has advantages over Norton but speed and size are not two of them, as it is about as slow as Norton. All four of these products have firewalls built in, just like Norton, so they are apples-to-apples. Two others worth mentioning. Zone Labs has recently introduced its security suite, which is basically Zone Alarm plus a rebranded version of Computer Associates' eTrust EZ Antivirus, a quality and very fast and slim antivirus program. Of course EZ Antivirus alone would be apples-to-oranges, because it contains no firewall -- although Computer Associates, having partnered with Zone Labs, offers its own security suite containing a rebranded Zone Alarm. Stick with Zone Labs, however; they are cheaper and have better support. The final option worth mentioning is Authentium's new antivirus+firewall solution. It includes Command Antivirus, which contains the very good F-Prot scanning engine (again, F-Prot alone would be apples-to-oranges) plus a firewall.
Finally, there's the apples-to-oranges comparison. These options are good for people who want to use both antivirus AND firewall software. This is probably the best setup in many ways, but it does involve installing two programs. A very highly respected AV product is NOD32. Its scanning is highly accurate, even for many unknown threats, and it is one of the smallest, fastest, most compatible programs out there so it won't adversely affect your computer performance. NOD32 has a good reputation among power power users but its interface isn't all too intimidating. Similarly small, sleek, and fast products include F-Prot and eTrust EZ Antivirus (a.k.a. Zone Labs' antivirus solution), already mentioned above. Command Antivirus, which uses the F-Prot engine, is also quite popular in corporations and schools if not as much with home users. Another ultra-high-quality scanner is Antiviruskit, which like F-Secure uses two high quality scanning engines at once for even greater security. The downside with it, as with F-Secure, is that its scanning is a little slower. It does not slow down the system, however, to the same degree that Norton can. Sophos is a good option as well. They are well-known for providing about the best customer and technical support in the industry, so if that is a priority they are worth considering. Their scanning is solid as well although the interface (and perhaps even overall design) of their program could use some work. Many of the smaller companies have decent tech support, so if that is important, don't even think about Norton or EZ Antivirus, and probably skip McAfee as well; go with a product like NOD32, Sophos, or Command.
Good firewalls to throw on top of these babies include Outpost, Zone Alarm (about the most idiot-proof, but also a bit large and with a handful of compatibility problems), Look 'N' Stop, Kerio, and Sygate. If you use a robust firewall along with a sleek and trim AV scanner, you're once again not comparing apples-to-apples because you'll have a better firewall than what comes with most of the basic AV security programs.
Can't forget about the ever-popular free scanners. The three real contenders here are AVG, AntiVir, and Avast. Of these three, AntiVir might have the scanning engine I trust the most. It's actually used in commercial products like AVIRA (another way they make money). Its interface is a bit dated looking but it's functional. Avast's interface is downright weird, but its scanner is OK. AVG is quite popular and its protection has historically only been OK but it has improved a lot and is now pretty robust.
Also, a final couple of products. SystemSuite is a utility product that uses the same AV engine that PC-cillin uses plus the same firewall engine that Sygate uses, so that is a pretty good all-in-one option that also includes a bunch of other utilities that could come in handy. System Mechanic is a utility suite that uses the Kaspersky antivirus and firewall components, and also comes with some other goodies, so that should provide relatively solid protection too.
Yes, this post is pretty mammoth. I have no particular agenda. For full disclosure, I use EZ Antivirus, which I more or less recommended you not buy merely because CA's support is shoddy. The scanner itself is good, however, so if you want to go with this one buy it from Zone Labs.
And no, mine is not the final word by any means although I have tried to provide a good overview. I hope it will be useful to someone. Clearly there is no one right answer here, but fortunately there are plenty of quality products by now. Note that you have to take detection tests with a grain of salt. Most of them are misleading in one way or another. The Virus Bulletin tests are the de facto and quite useful, but realize that a program might have failed 10 times in a row but then passed the last five times and only be 5/15. As some companies have made huge strides over the last few years, this can be misleading. Also, tests that only show how many viruses a product detects can also be misleading. Some of these viruses are either obsolete or were never released in the first place. When I say a program has a great scanning engine, I base that on trying to reconcile what I've seen with a common sense analysis of it. As of now, the best scanning ENGINE is probably Kaspersky's. However, if that is true (and it is hard to judge for certain), it is true only by such a small degree that most users will never notice a difference and I would not recommend you base your decision on that. Everything I've mentioned is quite capable of protecting nearly everyone. And it's important you get a scanner that you know how to use properly and that works well with your system, because otherwise it's nowhere near as useful.