Favorite perks for supporting members would be the ability to have unlimited time to edit posts. I know I always end up finding errors in posts long after I am able to edit them as a free member. Also, the supporting members exclusive giveaways seems like a nice perk/reason for becoming a supporting member.
7/14 I like the idea of a custom title.. that could be fun..
you should do something like board game geek where you can have little icons under your name with specific interests. So, a wrasse lpver could have a,little wrasse icon..