I had an interesting idea, although I haven't the time or inspiration to complete it.
So, what is this idea? Zoo Tycoon!
Obviosly,it couldn't be as complex as ZT2, but we could likely get a fairly quick prgm similar in feature to the original. We could even use this as a way to design the first true (in my experiance) expansion pack, because that would be cool.
Sorry about spelling errors - I wrote this on my iPod.