Not all wi-fi cards and usb dongles have built in linux support though you cna get almost any of them to work with a bit of fiddling.
A plug and play card or usb is your best bet though.
https://wiki.archlinux.org/index.php/Wireless_network_configuration#Installing_driver.2Ffirmware
https://help.ubuntu.com/community/WifiDocs/WirelessCardsSupported
Some more very useful information here,
http://www.reviewlab.com/best-wireless-adapters
I have a PCI card that cost less than £10 and it works fine for me and have some usb donggles that were less than £5 that work well too. They are all slower than todays standards but I do not do a lot of streaming.
Really you would be best getting something that had the latest "ac" connection and USB 3 if you are getting a dongle.