Basic Karcher stuff is OK in my experience. You should fork out for the patio attachment though as the wand is strong enough to destroy grout and leave stripes on stones and wood.
(At the strongest setting it's powerful enough to strip paint from wood).
pressure washers - talk to me. are the £60 bosch/karcher ones crap or do i need to be spending >£100. occasional use only for cleaning patio etc.