HS33s: http://www.wiggle.co.uk/v2_product_detail.asp?ProdID=5300004275

A much cheaper option is a set of V brakes:

http://www.wiggle.co.uk/v2_product_detail.asp?ProdID=4000000778

I find Vs far too flexible and spongy though (yes, I have tried XTs and XTRs, boosted as well) as I like a very firm modulation. Hydraulic brakes take a little getting used to as they don't have the snap back when you let go of the lever since there's no spring to do so, just the hydraulic pressure pushing the lever back, and they feel loose when you first touch the lever as you've no cable resistance to work against. The upshot is that you can feel much more accurately what they're doing. This is, of course, personal opinion.

I've found some discs to feel spongy, but I believe this to be poor setup, causing one pad to come into contact with the disc first, and flex it over until it meets the other pad. This will rapidly lead to disc warping.