If you're looking at a desktop, Asus or Lenovo. STAY AWAY from HP and Dell at this point. Familiar names, but unless you're getting into their business lines you're buying garbage. At Best Buy we don't have any Asus i7s in store, but I believe we can get you a Lenovo with one for a decent price. And honestly, if you can get a computer with an i5 2500k you'll probably be fine.
Macs are great, but only if you wanna pay 3x more that the Asus or Lenovo.
If you want a laptop, stick with Toshiba. We always have good deals on them. Just keep in mind that if you go above or below a 15.6" screen you'll pay a premium for portability or "entertainment" value. 15.6"s are most popular and therefore least expensive. My money though, I'd buy a desktop and then buy an iPad if you're really looking for portability later on down the road. Call me at 4799739524 then 8 then extension 2170 any MWF or weekend afternoon and I can do some snooping for you, check inventory and sales and the like.
My last computer was a Tosh (and it still runs after 4 years), and my wife's is, and my F-i-L's is, and my sister in law's computer is... but I just couldn't get over hte cheaper feel to the new Toshibas unless you step up to the nicer Portege model ($750+). The Asus U series (U56 = 15.6", U46 = 14") have some aluminum in the body, and just felt higher quality build to me. Also, mine has a fairly standard keyboard layout, longer battery life, num pad, and is very slim.
The Core i5 has been very fast to me, for what I do with it, watch movies, listen to music, word processing, Excel, and web browsing. With the battery life, I can take it to work and not have to plug it in all day. It has HDMI out, for external monitor or TV use, USB 3.0. That's all I needed.
My IT guy also highly recommended the Lenovo computers, and I very nearly bought one of them, until this one went on sale, and had the same specs as what I wanted for $100 cheaper. Also, didn't have the model I wanted in stock.