Yeah, it completely depends on what you are looking for... If I'm too lazy to make my own begging, looking through the ferret bedding on eBay si always a good bet. The low priced stuff is usually made by people who aren't seamstresses or who don't have a eBay store dedicated to bedding. THeir stuff isn't perfect a lot of the time, but the price is low, and with rats, well, they destroy it quickly enough anyway.
Cages are always good to look for second hand, and for toys and random stuff like that, I've found that looking in the bird section always turns up something useful. ^^
I look around eBay often for rat items. I used to search for "rat" in the small animal category, but I found I'm better off browsing the entire category to find stuff that works well. I also check the bird toys (got a huge lot of really nice toys for a good price) and ladders. Sometimes, I'll look at the cat ball lots and toys and the dog toys as well.
I didn't have anything particular in mind, I was just sort of wondering what everyone's experiences with getting rat stuff off of eBay was like. After posting this I ended up finding and buying a wheel, blankets (for bedding), a basket of fun destructible things, and one of those wicker-type nest balls.
I can see this is going to turn into a very expensive thing for me.