For me the overall best blades are AstraSP and Personna - they seem to work in the largest number of razors, are sharp and very smooth and are reasonably priced at around £8-12 per 100.
For out-and-out sharpness, it's Feather, but I only get 2 decent shaves out of them before they start tugging, so I keep a few in for when I have to look my best, and stay stubble-free for the longest. Morning weddings that go through to the evening reception, that sort of thing.
Best value for me are the SuperMax Blue/Orange&Blue (as I've mentioned at length elsewhere), but with the caveat that they seem to need a heavy razor to get the best out of them - a lightweight razor like the Tech or Boots own-brand (that both work well with the Astra/Personnas) just doesn't suit them and makes them "bounce" off the stubble for me. £6 for 200 is as cheap as chips though.
I've tried plenty of others - Dorcos, Derbys, Treet, Trig and Tiger were all ok, but at the same price as Astras not in the same league, and Lazers were just plain awful.
Edit: (7th March) - saying that I went back to try a Treet durasharp this morning, and it was like a scene from Psycho. I think I'll be avoiding them in future...