I wrote this for a friend last week, but it should be helpful:
The only thing that really matters for a new laptop is the processor (and weight and battery size). If you go Intel, ou want a new Intel Sandy Bridge Laptop. That includes i7, i5, & i3 -2000M series CPUs. I have separated the CPUs by price tiers:
You won't notice a performance benefit of anything better than the 2630QM (that's what I got my wife). It will cost you several hundred dollars to upgrade though. No other i7 CPUs are good because they are either low power (slower) or they lack hyperthreading (4 threads only instead of "true i7" 8 threads).
i7-2620M (even faster, and not a "true i7)
These will get better battery life than i7's. Just like the i7's, the slowest of this bunch will be capable of more than it will get used for. Unlike the i7's, the upgrades aren't so expensive as to be completely out of the question.
It'll do everything you need quite well. Battery life should be similar to the i5-2410M.
Any laptop will also list its graphics. Intel HD 3000 graphics is adequate. Fancy discrete Radeon or GeForce graphics will help you play more 3D games though. A Radeon 6630M is roughly equal to a GeForce GT 540M. And any number higher than those is better than those.
AMD/APUs: If you're really interested in budget gaming on a laptop, AMD's Llano processors (APUs) recently came out. They're basically Phenom II's with attached mid-low graphics. They can play just about any game, but only on low. These CPUs will be slower than the i3-2310M, but perfectly adequate. They really are only worth it if you're into gaming on a budget and it hits the right price point. Otherwise an i7 w/ discrete graphics would be a better buy. These AMD APUs (Accelerated Processing Units) get better battery life than Intels while gaming.
You also don't need more than 4GB of RAM because it's very cheap to upgrade ($25 currently) and you won't notice a performance difference anyways (unless you run virtual machines or do a lot of work in Rivet).
The business lines (Vostra for Dell, Thinkpad for Lenovo) tend to be built a little sturdier. Some people also like higher resolution screens so consider "full HD" 1920x1080 and "HD+" 1600x900. 1366x768 is "720P HD" and typically adequate (what I got my wife), but lower resolution than a standard desktop monitor.
Hard Disk Drives (HDD): It's hard to say what size you need. My wife's laptop has a 640GB 7200rpm drive. The important thing is that you get a 7200rpm drive over a 5400rpm drive. You'll notice the speed difference.
Solid State Drives (SSD): This use less power, are shock resistant, and are MUCH faster than standard HDDs. However, they are MUCH more expensive. It's worth upgrading yourself if you want one (~$100 for 60GB, ~$200 for 120GB), but manufacturers always overcharge for including one.