I'm due in January too, and I'd like to suggest that you join www.diaperswappers.com. Not only can you find cheap used diapers there on FSOT, but there is also all sorts of information about the various kinds of cloth diapers. I'll try to summarize a bit of the basics below:
1) Prefolds, flats, prefitteds and countours -- These are basically like your old-fashioned diapers. Pfs and flats are essentially flat peices of material that you can fold into a waterproof or water-resistant cover. Prefitteds and countours are like these, but are shaped so that they do not require folding. These diapers are generally pinned, snappied or used with a cover to be secure on the baby. Pros: They are cheap, versatile and wash and dry easily. Cons: You have to fold, fasten and cover them.
2) Fitted Diapers -- These diapers look quite similar to disposable, but are much cuter and come in a much wider range of styles. Like the first category, they are not waterproof and will require a cover if you want to avoid leaks. Pros: They dry fairly quickly, come in all kinds of cute prints, are easy to use and versatile. Cons: They are not waterproof so if you have a heavy wetter you have to cover up the cute prints with a cover. (I am planning to use mostly fitteds and prefolds and go coverless around the house)
3) AIO/AI2 diapers (all in 1 or 2) -- These diapers do not require a cover because they have an internal or external layer of a material called PUL which is waterproof. AIOs have an internal soaker pad sewn in while AI2s have a fully or partially external soaking pad. Both are pretty much like disposable diapers. Pros: They are very easy to use. Cons: They take FOREVER to dry. (AI2s dry faster than AIOs)
4) Pocket diapers -- These diapers look like covers, with waterproof material on the outside and a thin layer of absorbent material on the inside. What people like about them is the fact that they contain a pocket which can be stuffed with doublers so that you can customize the diaper to your child's needs. Pros: They are waterproof, versatile diapers with a short drying time. Cons: You have to stuff them before you put them on the baby and unstuff them when they are soiled. This can be easy or hard depending on the type of diaper. Some pockets have very specific drying and washing instructions.
5) Covers -- There are 4 basic kinds of covers 1) PUL, 2) Vinyl, 3) Fleece and 4) Wool. The first 2 are waterproof and the last 2 are water resistent.
6) Doublers and liners -- Doublers allow you to increase the absorbency of your diapers. They are often made of microfiber, bamboo or hemp. Liners allow you to wick moisture away from the baby's skin to avoid rashes and to minimize mess (lkie meuconium poo).
I would suggest that you first figure out what kind of dipe you're looking for, and then you can navigate all of the brand names. Check out www.diaperpin.com for reviews of various diapers. Ebay has a decent selection of diapers sometimes, but hunt for reviews before you buy. You can also check out craigslist, www.etsy.com and www.hyenacart.com (I like the spots corner for used diapers). You can also order WAHM (work at home mom) custom diapers once you figure out what basic kind you think you'll like. Both Etsy and Hyenacart have a ton of options.
Your baby will probably be in NB sized diapers for the shortest time of all, so you might want to get a combination of NB and SM sizes. I have a ton of One Size diapers which, although bulky on a newborn, will fit after the baby is about 10 lbs or so. If you use covers, try to find NB covers that have an umbilical dip. I like Prowraps and Imse Vimse.