Most people will probably recommend the monitor they’ve got. However, I would like to make a point that I think is often overlooked: the W/H ratio of the usual 16:9 monitors is not ideally suited to the display of photographic images with ratios of 1:1, 4:3, 6:4 etc. For these ratios the screen height is the limiting factor and the screen’s full width may not always be usable.
A 16:10 monitor is better unless you have the money or space to buy a huge 16:9. I recently bought the Dell 2410 and am very pleased with it. A full-screen 6:4 image displays at 45 x 30 cm. This machine comes within your €500 budget (although sites like the one below list it as more expensive). It also meets your other criteria.
You may find this web site useful in your search:
http://www.tftcentral.co.uk/selector.htm
Good luck.