Reusable swim diapers are great. You don't have to be a cloth diapering family to use them since you just throw them in with your regular wash (flush any poop first!). Even if you cloth diaper you shouldn't wash them with your diapers because the chlorine from pools can be damaging.
Swim diapers work very differently from regular diapers. They are not absorbent. I repeat... THEY ARE NOT ABSORBENT. This goes for both reusable and disposable swim diapers. This trips a lot of people up I think (me included!). Don't put a swim diaper on your baby until right before you go in the pool/lake/ocean/whatever. They are only meant to contain poop. Pee will leak right out of them.
There are quite a few different brands that make reusable swim diapers. iPlay, Bummis and Apple Cheeks are just a few.
I wish I could get Ant more on board with these. I think they're really neat! He however, likes his throw away Ziplock bags he takes to work. We got this bag free with a cloth diaper order a few months back. I wish it had a zipper closure though. After I ran it through the dishwasher there were some food particles stuck to the Velcro, yuck! I did a quick Amazon search and other brands to make zipper ones if that's more your style.
Just like reusable cloth diapers, they make reusable pads for mom. Affectionately known as "mama cloth." :) Some cloth diaper companies, like FuzziBunz and Swaddlebees/Blueberry make mama cloth as well.
I've personally never tried mama cloth, but I know lots of ladies swear by it!
I like the idea of transitioning to cloth training pants instead of using disposable ones. I haven't done any research on cloth training pants so I don't know which brands are best or even how they work. I've got a while before I need to start really looking in to them, though :).
There are of course a bagillion other ways you can go green, but I thought these four would be the easiest to try for cloth diaper families.