Ive used WCS ones in the past, but i also found them too fat and they spun round in the rain (never had that problem did you MTT, riding in the rain that is ;0)
Ive also used super thin ones which i pulled off one of those hand strength gripper things, they were ace! loads of feel (ie. no cushioning, tho everyone on here says 'feel' or 'feedback' from your frame is a good thing so i cant get flamed for that!) but in the end they wore out too quickly. Incidently they look exactly the same as the nitrile ones poshbikes sell as another mate now has some of those.
What i use now tho is ergon GX1's, so much better! they add a good bit of comfort over normal grips with the added control over your whippet like bike on the downs, seriously, one of a few pieces of kit ive bought (like a stiff stem and forks) where performance won out over weight!