I recently bought a laptop, so I shopped them a lot… You simply have to know the specs to compare them.
First of all, you have to know what kind of laptop you want:
10" - 11" - Netbooks, very small, often good battery life, but no specs at all.
12" - 13" - Light laptops… when those have good specs, they cost a crapload because you get specs + portability in the same package.
14" - 15.6" - The usual laptop, those often offer the best specs/price ratio.
17"+ - So large, I’d avoid those.
If you could tell us your budget, it would help a lot too.
Then, let’s take care of the ram, since it’s so simple. You want at least 4gb of ram, I don’t suggest you get more because getting more than that implies that you get 4gb of each stick of ram, which makes it very expensive… 2x 2gb of ddr3 is the standard these days. Also, it often costs about 20$ to upgrade from 3gb to 4gb, you want 4gb of ddr3 ram.
Now the cpu… I use intel… so that’s what I know. The new intel branding is very, very confusing, here’s how it goes:
Core 2 Duo are the last generation of the intel dual cores… they are getting cheaper, they are good, but generally, a core i5 would be better.
The i3 are the low end new dual core processors, they faster than what it used to be, but an older high end Core 2 Duo will probably be faster
The i5-450M, i5-520M, i5-540M and i7-620M are the new high end dual cores, these cpus are the fastest dual cores out there, to give you an example, my i5-540M, 2.53ghz runs about as fast as an older core2duo at 2.93ghz…
The i7-720QM and up are the quad core cpu for the laptops… they run at a lower clock speed, but they are quad core, they often mean the laptop has a very low battery life.
I have a Sony vaio CW, I like this machine… they stopped making it really fast… they replaced it by the EA I think, they are 14" machine… These are like the home versions of sony machines… they aren’t as great as the Sony Vaio Z, but at least I could afford it.
By the way, if your budget hovers in the 2000ish… consider a Sony Vaio Z, they are really nice machines… 13", great specs, great build.
About the brands, I’d say away from gateway, acer and toshiba. I heard Asus is pretty trustworthy… Buy a laptop is a hard choice, so many choices, yet none of them will fully satisfy your needs, you have to set your priorities.