This is an easy one, as I'm currently pouring over reviews myself for new monitors for home
If you want 20-21" widescreen, I'd go for either the NEC MultiSync LCD20WGX2, or the Samsung SM-215TW. The NEC has apparently superb black level and colour rendition, due to a high gloss screen. If you don't like that type of screen, then go for the Samsung which has a conventional anti-glare coating. Both use S-IPS panels, which is what you want to be looking for if you're doing photo editing.
I'm a great fan of the NEC S-IPS panels, as I bought a load of 19" 1980FXi and 1990SXi units for the office, and they're pretty much the best there is in terms of static image quality (but not cheap at £430!).