I don't really race much anymore (too busy evading park cops out on the Monon after dark), but here's a few that I recall being more competitive..
Dick Lugar 10k in early Sept - sub 33:00 winner last year
Pleasant Run Run 5 miler Oct - 5:00 pace winner last year, has been faster in previous years
Jingle Bell 5k - early Dec, 15:08 winner last year
Shamrock run - St. pats Day -- someone good must show up?
I'm sure there are more. There are some summer track series (Zionsville -- see runz.com) and also Bob Kennedy's place put one on as well at IUPUI, not sure how fast these races are going (the z-ville ones are pretty slow...though you might be able to run a fast mile up there).