For a speedtest I use:
pcpitstop
At one time, I was getting download speeds of only 150K when testing using this. I phoned NTL to complain, and they asked me to confirm how I was testing my connection speed. When I told them I was using pcpitstop, I expected them to say that it wasn't reliable - but they didn't, they just told me that they had 'just noticed' a fault, and it would be fixed.
Guess what - it was fixed - now I never seem to get less than 300K (with regular peaks at over 500K). Not ideal, but good enough to prevent lag on Live (don't host often though)