Shoothill have added to their flood warnings map a new live river levels map

http://www.gaugemap.co.uk/

The original flood warnings map is still operational

http://www.shoothill.com/floodmap/

Both sites well designed and easy to use

P.S. England and Wales only - apologies to the other home nations

I'm impressed the stations are 'tweeting' a daily report so you can follow ones of concern to you.