You know, I think I just googled "childbirth preparation" and my location and looked for stuff that came up. Reviews and such, you know. I also looked at the information the hospital I was going to (active duty, so no choice there) had, and they had a list of a bunch of places that do childbirth education. It was part of the OB intake packet.
I would start with a few books, though, because they're not as expensive as classes, and you can get them from the library. I do NOT, under any circumstances, recommend ANY of the "what to expect" books, as they are... well, IMO they're depressing and unnecessarily alarmist. And the Toddler book was horrible. I thought it was geared towards the best way to guarantee the Two's were Terrible instead of just, you know, part of growing up.
I highly recommend reading Ina May Gaskin's Guide to Childbirth, the Dr. Sears Pregnancy book, the Dr. Sears Baby Book, and the Happiest Baby on the Block (Also, the Happiest Toddler, when you get to that stage). They are all very affirming books that don't make you want to second-guess everything that you are inclined to do just naturally. They aren't alarmist, and they have a lot of practical information. Birthing From Within focuses on how to get past your fears about childbirth, (or, even about the *Care* you'll receive) which I think would have been useful for me the last time around, so I'll be following some of that book's stuff, too, this time.
With less enthusiasm, I also recommend Henci Goer's Thinking Woman's Guide to Birth, and Ina May's Spiritual Midwifery. The first because I found that it made me just a tad too suspicious to be able to relax in company of medwives or OB's, which was necessary for me to be able to give birth the first time. If I'd been blissfully ignorant, I might have been able to relax and have my baby. As it was, I was so wound up and suspicious, I ended up with an "emergency" c/s that I didn't want and didn't need, but was coerced into anyhow, even knowing that at the time. Spiritual Midwifery because, honestly? It's just TOO too hippy for my taste. I don't want to read about "psychedelic birth waves" and stuff, and that's all that book made me thing about. I couldn't get past it. But they both do have a lot of good information, and many other women find them useful.