Large laptops (17" and above): These laptops only really have one thing in common: they're big and usually heavy. They aren't super portable, are easier to carry around than a desktop computer, and they range in price from $500 or $600 to over $2000. The cheaper ones are usually low-powered and useful for people that just want to watch movies on a bigger screen but don't plan on carrying it around. The more expensive ones are more geared toward gamers and professional photo or video editors and come with all the power you'd need to perform more complicated tasks.
Midsize laptops (13"-16"): These laptops are your all-around, affordable laptops for the average user. They have a pretty big range in price and power, so you can almost always find what you're looking for. You'll find most of them lie within the $500 to $1400 price range, and they're great for people that want a simple laptop but want a lot of USB ports, a CD drive, and other perks without paying a lot of money. They're more portable than large laptops, but still will carry a noticeable heft in your backpack at around 4-6 pounds.
Full size
Ultrabooks (Usually 14" and smaller): If you're willing to spend a bit more money for extra portability, you can get an ultrabook, which is a super slim, super light, moderately powerful machine built for the average user. We've talked about them at length before, but these are great if you're willing to sacrifice a few USB ports and a DVD drive in the name of portability. They weigh about 2-4 pounds, cost closer to $1000, and carry enough power for all your basic activities and maybe a bit of light video editing.
Small laptops and netbooks (Usually 12" and below): These are ultra cheap, ultra portable, and ultra low power. They're really only good if you're looking for extreme portability, and are willing to sacrifice quite a bit of power to do so. Don't expect to do more than simple web browsing and email on these machines, and even then, you can expect it to have a bit of lag to it. Still, at about a $300 price point, it'll get the job done without breaking the bank.
Most people right now are making the decision between a midsize laptop and an ultrabook, and it's a tough decision. Midsize laptops are going to offer you a ton of choices, so you may be able to find the perfect laptop there, and for quite a bit cheaper than a comparable ultrabook. That said, we're pretty stoked about ultrabooks around here, as they're virtually weightless and more than powerful enough for most people. If you're willing to plop down the extra cash and ditch the DVD drive (which you could always replace with an external one), they're worth a look.
http://reviews.cnet.co.uk/laptops/samsung-series-7-700z5a-review-50004913/
2012 winner
http://reviews.cnet.co.uk/laptops/asus-zenbook-ux21-review-50005601/
under 500 see http://reviews.cnet.co.uk/laptops/best-laptops-for-under-500-49290158/