Dell will very often give you the most bang for your buck, especially if you buy through the
Dell Outlet. However, if you're willing to wait and hunt for bargains, you can often get Dell prices or better from a number of other brands. Also note that $2000 is a lot of money for a laptop these days, and it gives you a whole lot of options for the specs you mentioned or better.
Apple and Sony both generally manufacture the best looking and most overpriced systems. Apple laptops of course come with Mac OS (for better or worse), and Sony laptops have the added feature of being a little more fragile than other systems, and generally being harder to repair (on the hardware side).
My current laptop is an Acer. When I got it about a year and a half ago, Acer and Toshiba were my top brands. These days, Acer systems generally don't interest me because most current models have AMD CPUs (for the time being, Intel chips are superior).
So I'll put in another vote for Toshiba, my current favorite. The other biggest contenders are HP (also a good option), Gateway (not too exciting, usually, though they offer some nice Tablet PCs), and Lenovo (good for business users).
Think about what you want, beyond the basic specs you've already mentioned. For example, screen size. 15.4" diagonal is standard, as well as generally the cheapest configuration. Any smaller or larger will typically cost extra. I like slightly smaller systems (since I rarely use my laptop for multimedia or gaming), so I gravitate towards the lighter, smaller 14.1" systems. Keep in mind that individual manufactures don't offer every screen size available. For example, if you want a 13.3" screen (generally the smallest size practical for every-day use), Sony is probably your only option, though a number of manufacturers offer 12.1" and smaller. 17" systems are also very common, and some manufacturers offer systems with 20 inches of screen real estate or more (these are both expensive and heavy).
Will you use your laptop for gaming? Alienware (owned by Dell) and Dell offer some of the best gaming laptops, though they're generally not practical to carry around regularly.
Are you interested in a Tablet PC (which use screens that can be rotated 360 degrees and accept touch/pen input)?
If you want a really light system, usually the biggest factors are screen and battery size, so if a system is offered with multiple battery configurations, you might want to look at that (of course, a smaller battery also means less running time, as well as generally lower price).
After filtering down your system by price point as well as more specific features, the number of systems available should be a lot lower, which should make the decision that much easier.
Finally, if you're getting a Windows system, the best option by far for most home users is Vista Home Premium, unless you
really want the extra (mostly business-related) features in the overpriced Vista Ultimate.