After Effects doesn't use the GPU for much. See this post: GPU (CUDA, OpenGL) features in After Effects
The After Effects System Requirements for Mac OS and Windows page covers what your minimum requirements are.
The one big feature that does use the GPU (the ray-traced renderer) is considered obsolete and very few people are using it anymore. See this post: http://motionworks.net/after-effects-3d-future/
If you really want to use the ray-traced renderer, any NVIDIA GPU from the 700 or 900 series will likely work in the most recent version of AE, but you may have to check the "use unsupported GPU" checkbox to enable it.
Some third-party plugins for After Effects (like Element 3d and Red Giant Universe) do make use of the GPU, but their requirements are completely unrelated to the outdated ray-traced render in AE.
If you use Premiere, you will want to check Premiere's requirements. Premiere makes use of the GPU a lot.