For general use Drontal Plus tablets, but if you want a liquid one Panacur 10% Liquid. I use the liquid for in whelp bitches and baby puppies, then go on to Drontal for older dogs. I only worm about twice a year, or if a bitch is in whelp.
Both can be ordered from any of the online veterinary suppliers, such as petdispensary, or hyperdrug.
The ones from the pet shops are not much good, and a lot of vets are now recommending Milbemax which I would not use as it can have bad side effects on some dogs, particularly collie types, although not just those.