There are pluses and minuses to buying a computer on the internet and at a store.
If you buy online, you can shop easier, don't have to deal with sales people, don't have to pay tax. But downside is you have to pay shipping, go through waiting, and you might have to go through a lot of trouble clearing things up if your machine arrives damaged or with other problems. Personally, I mostly buy online and experience so far has been good. You should also check out,
Clubmac
Smalldog
Macconnection
Maczone
Amazon
MemoryX.net (for RAM upgrade)
If you buy a computer at a store, you can ask (or convince) them to open and check for dead pixels, dents, etc on your computer. But the downside is you have to pay tax and sometimes service can be frustrating. I don't recommend CompUSA either because I find their people not very knowledgable about Macs and their sales tactics can get very annoying. I once bought an iPod at CompUSA and even bought their Return Policy because sales guy convinced me that if iPod broke down I will receive replacement, no questions asked. Well, iPod eventually broke down and when I came in for replacement, there were a lot of redtapes, the whole thing took over 3 weeks before I got a replacement. If you want to buy your mac at a store, you should go to Apple store.