Wellseal is meant to be up there but not always easy to find (also doesn't go hard), blue Hylamar is great, but for every day I just use a Loctite grey silicon product for things like primary sides. Seems to work quite well, and any small excess is hard to see against an alloy casing, unlike red, orange or primeval puce-coloured goop. But 'sparing' is right, nothing worse than loads of extruded gunge round every joint (and probably on the oily side as well).
The best other aid to a relatively leak-free life that I've found is a few rolls of decent gasket paper in various thicknesses, a modelling knife, a few of those sharpened, hard, tubular hole cutters - and not too many beers before doing cutting. A modest stock means you're never stuck and don't have to play with cornflake packets or brown wrapping paper. It really only leaves head gaskets having to be bought . . . which appeals to the mean streak in me too.