Tesco do a goats cheese with garlic and herbs which is great spread on the base - i then top with cheddar so not to keen on the stringyness of mozzarella
Mascarpone is absolutely delicious on a pizza. I buy a really nice chicken and bacon pizza from Sainsburys, which uses mascarpone. It is slightly sweet, and very creamy, so a nice alternative to mozzerella which can be slightly flavourless and rubbery at times!