Afaik GAME and Gamestation are the 2 best sites to buy from, understandably as they are the same company.
Both offer the bundle of £260 for the Wi-fi model with a 4GB card and a selected game.
Can't say I'll be buying a VITA anytime soon. It's doing a lot worse in Japan than the 3DS did at launch (VITA sold less than 20,000 units last week), and the 3DS failed epicly, so I'm being wary before i splash out all that. My knackered PSP will keep me running til then.