After Effects Filters?
 

In After Effects 7 Pro what blending mode should I use to simulate a filter on my lens? I am too cheap to buy any and I like keeping my options open until post. If its not as simple as just using a color solid and applying a blending mode to it then can someone please tell me what is the best way to do this simulation.

There are many many many ways to simulate filters, though (especially when shooting digital) it's often a good idea to try and shoot with the actual filters in the field rather than apply effects in post, since (unless you captured in something like cineon or OpenEXR) your adjustmenst are limited by the dynamic range of your digital files.

A post-processing filter will not be able to recover data lost in area of the frame that are over-bright, but an ND or polarizing filter on your camera can often help bring these areas into the capturable range.

To simulate color filters, a color or gradient layer with Multiply mode is certainly one approach.
You can also use the various channel and color adjustment effects (curves, levels, etc) directly on an existing layer if you like.

Good luck.