Actually, nowadays it's pretty narrow-minded to say that a laptop is crap for gaming. For example I have a pretty budget Toshiba laptop (I bought it for like ~800 USD two years ago) and it still runs newer games. The main problem is, that manufacturers see a bucket of money instead of people, that are willing to purchase a laptop.
The main specs are always "CORE2 QUAD 8000 GIGAHURTZ 8 GB RAM 1 TB HARD DRIVE OMG", but mostly forget to mention the graphics chip. But there are indeed deals, that can compete with desktop rigs. Sure, they're not upgradeable, but can serve you for 'round 2-3 years, if you're lucky. You just need to keep your eyes open, and look at the specs. Especially if your goal is to run like Source apps, you can get a laptop for 800 USD, and can use it for future games as well.
The laptop I have is a Toshiba Satellite A200-1S9, which - as I already mentioned - cost me ~800 USD two years ago, and serves me perfectly fine. It has a cheap Core 2 Duo processor and a fairly decent Ati Radeon HD 2600 graphics chip, and even in the worst case, I can run newer games - like say Borderlands or Mass Effect 2 - on high settings at 1024x600 with playable framerates. Yeah, it's not the highest resolution, but since the highest resolution is 1280x800, it's not a huge sacrifice.
Yeah, if you want to run everything on max resolution, with 8x AA and 16x AF, you should get a desktop, or a lappy for 'round 1500 USD. But if you just want something, that can handle everything with a minimal compromise and needs to be portable, hell, go with a laptop. Just keep your eyes peeled.