Yoyotech is a shop just off Tottenham court road, on Windmill Street (Central London). Generally pretty knowledgeable and helpful. They helped me select parts for my first build back in 2003. I've also found them to be really good with returns; I had a dead 3930K processor, and they managed to find a replacement (these were pretty rare for ages after release), check it worked in my board etc.
They have a bit of a price premium over Aria (Central London so what do you expect), but similar sort of people work there; people who know about computers, and have a decent idea of what's good and what isn't.