So I just found this awesome site to track my mounts. I don't think I could remember all of the mounts I have as I thought I had 75, but here they are:
Not quite sure how I'm going to get to 100.
It also looks as if the URL changes each time you tally your mounts, so the link above could go stale quickly. But a nice site nonetheless that allows you to easily see what mounts you need and how to get them.