[Omnirizon]

Why are you wanting to make such a quick purchase? If you can stand the wait, taking a week to survey the options will pay big dividends. I got a 1600 dollar Lenovo T500 for 1000 dollars buy taking time and doing some hunting. Check out Newegg for good deals, and use TheFind.com search engine to search all online retailers for good prices. Compare like to like, and take the displayed 'mark-down' with a grain of salt, since displaying a high initial price just so that it looks like there is a big mark down to get to the real price is a common tactic. Often times the manufacturer site itself has great deals on backstock type stuff. Ebay is, in general, not a good idea, especially if you aren't savvy with the hardware you are looking at.

Lenovo, Sony VAIO, and MacBook are the overall best. MacBook you will pay a premium for. The others can usually be found at better than retail prices if you hunt around.

* 64-bit architecture is a must if you want more than 2GB of memory
* 4GB of memory is the going standard, but 2GB is the max for 32-bit architecture.
* dual-core Intel is virtually the only option on the market. 2+Ghz is sufficient.
* non-integrated graphics is a good idea, but you don't really have much option in the brand. For a given price range, there are usually on two options, and manufacturers will just use one of these options in all their offerings. Ultimately, the only decision to make here is integrated or non-integrated graphics.
* Windows 7 is a must
* Disk space isn't important. External Disk space is cheap, so going with whatever you find, given that all the other options are right, is the best idea.
* 15.4 inch screen is standard. If this will be parked on a desk, go for 17+ inch and get a Numeric keypad too.

In general:
* 64-bit Windows 7 Home
* 4GB RAM
* 2Ghz dual core CPU
* non-integrated graphics (unless you do no gaming/media)
* 160GB HD

If you are a traveler with power needs:
I suggest a Lenovo T500

If you are looking for a Desktop Replacement (DTR):
I suggest a Sony VAIO AW. It is an 18.4 inch screen (the biggest around). Screen size is cheap, so really it doesn't cost any more than a 15.4 inch.

If you just want something portable:
Something from the Lenovo IdeaPad line, or something from between the Sony VAIO SR and FW series (depending on your screen size / power needs).