Okay, so short story time.
Before we launched the site I was juggling the idea of having a badge for donations. However, because the badge system requires us to manually input the recipient every time, individually, we quickly dropped that idea in favor of the current membergroup system. However, we did shoot back and forth the idea of a more exclusive forum donator award, which would include a possible badge.
As of this point, I am against adding more membergroups. We already have several, and I would prefer to keep the more important ones as visible as possible. I do think that we can do something about a special donator badge. Perhaps one that is given out to the person who donates most, and it can be a sort of competition. Possibly we can create some tiers of badges as well.
Good Suggestion, I will bring it up with the rest of the team and see what we can come up with.