I tend to google for ideas, I found an american website and the bbc good food had loads of ideas. The best things I have ever cooked in a slow cooker are joints of meat with very little juice, the meat just falls off its amazing. Pork with a cup of apple juice and chopped apple, lamb with a cup of stock or wine and gammon sat on a bed of veg with a cup of cider just covering the veg. Have fun experimenting.
The Slow Cooker Cookbook by Gina Steer It's not too American as some are - (nothing against our cousins across the pond but I find US recipes with their cups and weird ingredients a bit annoying when I'm trying to get dinner on the table tonight...)
There are some recipes that I'll never make (pate? individual desserts?) but lots of firm favourites (squash soup, rose chicken, duck jambalya and goulash)
What I've found most useful though is that there is huge variety of recipes so if I'm making something entirely different/adapting a regular recipe/making it up out of my head I can usually find something in here sufficiently similar to use as guidance for timing and method.