Most laptops out there will support OpenGL to some degree. It's not a matter of having or not having OpenGL, but rather a matter of having the required OpenGL capabilities.
A laptop in the $400-600 range will probably be lacking in more areas than just OpenGL/graphics card. It may also not meet the requirements in terms of processor power and RAM memory. And this would be more important than the lack of adequate OpenGL muscle.
That said, if you find in that range a computer that has a 2 Ghz Intel Core 2 Duo procesor or higher, 2 GB or more of RAM, then it's worth pointing out that OpenGL is a bonus, not a definitive requirement to run the application. You will still be able to use it, you just won't get the kind of smoother/more responsive interactions that OpenGL previews can give in some circumstances.
Open GL is not mendatory but for one effect which is the cartoon effect. And i think that pixel bender plugins needs open gl too, but i'm not dead certain.
OpenGL is a feature you can easily forego if it's just for Adobe apps. The way it's implemented in AE or PS adds so little to your workflow, you will not notice much the absence of it. Recommending a specific model would be impossible - differnt models are sold in differnt regions and new ones are coming out every week. Just get the one you think will give you the best bang for the buck based on more generic research on hardware testing and rating sites. As noted, sufficient RAM is more important than other factors, so you may need to compromise on your budget here and there and e.g. go without a BluRay drive or a slightly older/ weaker processor...
> Open GL is not mendatory but for one effect which is the cartoon effect. And i think that pixel bender plugins needs open gl too, but i'm not dead certain.
No, OpenGL is not required for Pixel Bender plug-ins or for the Cartoon effect (which is written using the same underlying technology as Pixel Bender plug-ins). The Cartoon effect is certainly much faster when you have a graphics card; if you just run it on the CPU, it's quite slow.
In all cases, things that can run on the GPU (the chip on the graphics card that OpenGL is making use of) can also fall back to running on the CPU.
Personally---as Sebastien suggested---the Cartoon effect is the only thing other than interactive previews that makes me glad to have an OpenGL-capable GPU.
Thanks for correcting me Todd. I don't even remember why I thought they were open GL exclusive.