Found this posted on TMP (The Miniatures Page). An interesting idea for what looks to be reasonably attractive, cheap do-it-yourself river sections. I hope the blog owner doesn't mind me sending extra traffic his way.
Essentially, he uses cheap vinyl tile as his base and some silicon caulk for building the banks.
Personally, I think cross-pollination of blog ideas like these are a great thing. The more exposure to good terrain tips, the better, I say.