Best tip for potato bake is to over-season it. Potatoes can handle plenty of salt and once cooked for a good hour, the salt loses its intensity and because there are few flavours for the salt to bring out, it doesn't do a very effective job. Taste to preference before cooking, then add more salt and bake.
I like to make a few variations of potato bake:
Parmesan potato bake
Ordinary gratin dauphinois recipe but instead of putting cheese on top (as most people do), I make parmesan crisps (just melted parmesan that has hardened) and add them on top after the potato bake has cooled (to avoid the crisps losing their crunch).
Roasted garlic potato bake
Again, same recipe but instead of raw garlic, I roast a few heads of garlic and squeeze it into the cream mixture.
A few other things I have tried involves adding different herbs, such as fresh origanum, adding mustard, using creme fraiche and cream, pouring over a little stock before cooking, adding breadcrumbs to the top, using brown onion soup (yes, from a packet - it does taste good), or just making a cheese sauce (such as a mornay sauce)...