Lee most of the shop bought groundbaits will work mate, especially if it is a hungry water, ie there are loads of fish! It could be worthwhile having a walk round and asking what other anglers are using.
However you could be a little bit cute andbuy a few ingredients and knock something of your own together. Stuff like vitalin, fishmeal, plain brown crumb, molasses, micro pellets, various forms of maize and also hemp can all be otained for far cheaper than the £3 or so that you're paying for branded g/bait. Although it might cost a bit more to begin with, after 5 sessions or so you'll have saved a decent sum of money.
However for branded groundbaits, Sonu groundbaits work well for carp, I have also used Van den eynde expo for carp too, and the explosive feeder (by VDE I think) was excellent.