The housing registration opened in February, and most of the connected or close-in hotels are booked. Your best bet now is to register for a badge and get your name on the Housing Bureau's wait list for a close in hotel (many people have gotten good rooms this way in the past), or get a room out near the airport and cab into downtown Indy.
There is plenty of advice to be found on the Gen Con forums:
Forums - Gen Con LLC Community including an area to post "looking for rooms or roommates" threads.