I have a Samsung R580, with an NVidia G 310m and it is very good. However you need to get a balance. I have the latest Core i processor so the card performs better. You need a good processor and at least 3GB RAM to play the good games. I usually run my laptop with a 3GB RAM limit, and the card will run CoD4 on high specs and I can put Batman Arkham Asylum to the maximum. However the card eats electricity when doing this so if your gaming NEVER do so without being connected to the mains, or the performance is reduced significantly. With regards to Crysis, I tried it out on my laptop and it doesn't run very well at all, but in reality, if you want a laptop to run Crysis -which is unusual because it has its own graphics engine- your looking at the real high end mobility cards, in a laptop that won't be cheaper than £1000. All the above cards will run Crysis, but very poorly.
Personally I would recommend the NVidia card purely because I've got it and can promise that it works very well, given that the rest of your computers specs are good. What is the computer your thinking about?