Here is what worked for me when I had preschoolers.
1. MOPS--already mentioned by another mom. But it is all mom oriented, even though you have time away from the kiddos, you're still focusing on motherhood.
2. Bookclub--I was in a great bookclub with about 20 other moms. We rotated houses according to who had selected the book. It gave me a reason to spend some time to myself reading in the evening and a thought provoking discussion night to keep me mentally alert.
3. Crossword puzzles--I became the master of finishing the daily in 20 minutes. Coffee and the crossword is still one of my favorite things to do. If I can sneak off to Starbucks sans kids, great. If not, home is almost as good.
4. Ladies night out--We called ourselves Ladies of the Night. ;) Bunch of moms in the neighborhood who took turns hosting. The host was responsible for the activity and we all contributed snacks. We did country line dancing, game night, wine tastings, scrapbooking night, etc.
That was about all I did where I was without the kids. Everything else I still had the kids in tow, but if you do it with friends of similarly aged kids, it's still a bit of a outlet.
M.