I've been very pleased with my FujiFilm F10 and dedicated underwater housing. It's a great little pocket cam on land when I don't want to lug around an SLR and it has some features that make getting good underwater shots easier. You can see some shots I just took on Roatan, Honduras with this combo at http://www.flickr.com/photos/26660977@N07/sets/72157605108714797/

It's 3 years old, though, and I'm not sure how the newer models compare. An F100fd camera and WP-FXF100 housing look like they might run a little over 400 euro but there are probably some deals to be had on the next earlier model.

One of the key features to look at is shutter lag -- how long it takes for the camera to take the picture after you click the shutter release. The F10 has a high-speed mode that runs down the battery a little quicker but takes the picture almost instantly -- important with moving targets like fish!