Pretty much all new notebooks come with built in wireless capabilities. Most newer models come with 802.11 N, but some older models come with 802.11 B and/or G. Which standard it uses really isn't that important, but making sure the wireless router you get is compatible with that standard is(ie. If you get a notebook that uses 802.11 N and you purchase an 802.11 b/g router they won't work together).
When choosing the notebook it is really important to know what your son intends to use it for. There are several possible uses to consider:
Surfing the internet - If your son only wants to surf the Internet and run a few light applications, then a Netbook would be perfect. They are priced between $250-500.
Gaming - Typical gaming applications require more resources than standard computers, so its a good idea to purchase a more powerful machine. If you are budget-minded, I recommend the MSI GX 630 (Available at Amazon and Newegg). If you've got more money than you know what to do with, get an Alienware or Dell XPS.
Multimedia - Watching movies requires a decent integrated graphics card and a large screen. I recommend pretty much any 17" notebook with at least a 250 gigabyte harddrive.
On a final note, if price is a major issue, check out Bensbargains.net. They have links to a lot of great deals.