"cheap ones" haha, seriously tho, I think a lot of people use what used to be called "snee blue", they were 50p a pair. I think they can be had for around 1 quid a pair now, or 2quid for a full set.
When I buy then, I just buy rears and cut them down for front (2 or 4wd) when needed.
I am not sure who sells these foams at the moment though. I know BRM Motors (glyn ward) sells them at Nationals, but thats all I know
I charge all my NiMhs at 5 amps - I never discharge or do anything fancy. I charge, race and put away. I use packs maybe a couple of times in a race day depending on where I am / how many runs I'm doing. My cells are 2 years old mostly, and not the best, but good enough especially for 2wd.