Most preschools are registering NOW for next fall. A few might have openings for this year but most good ones have a waiting list. My advice is to start checking into them for next fall. Personally, we LOVE St Peters Preschool in Carmel. My son went for 3 years and my 2 year old is currently going. When my baby gets old enough, she'll go there, too. They start the moms day out program at 18 months and go through pre-k. It's on Carmel Dr just east of Keystone. Open registraton started last week.
The other option is for a daycare type place like Abacus. They aren't really 'preschools' but have preschool type activities scattered throughout the day. They are meant more for working parents and are alot more expensive because they are full-day program (like 6am to 6pm) and kids come and go throughout the day. They are open year-round, though.
Most of the preschools are run through churches (but they are not religious-focus and have pretty much nothing to do with the church) and follow the local school's calendar for holidays and summer vacation. The hours are set each day, like 9am-11:30am so there's a set schedule for all the kids -- everyone arrives and leaves at the same time. They are also much more affordable. A 3 day a week preschool program is around $100/month... but 3 days a week at a daycare type place is usually $100/week.