Make your own.
Poser and D|S use .png pictures to represent the figure/prop in the content menu / libraries. You can also browse them directly, if you know where to look in the runtime.
Really the only time I download other people's models is for Poser, but I think that having a little .png picture to represent 'content' models is a good idea.

Extending on that principle, make either small low quality renders, or do screen captures, of models and save them as .jpgs (or whatever) in the same directory that the models are in. Then you can just look at the pictures to get an idea of what the models are.

I do that with Wings3D model 'libraries'. I just take a snapshot when finishing up working on a model and save it.
3ds max generates a thumbnail of scenefiles (.max) automatically; but their are times when the thumbnail doesn't really do you much good, so in those instances, I use small renders and save them as jpgs.

Friends don't let friends use booleans.