I've been really into playing around with the lighter colored Belgian styles like Single, Pale, and Blonde (and to a slightly lesser extent Tripel and Strong Golden).
You can make some awesome beer with simple ingredients: blend of continental pilsner and pale malts, various sugars, a handful of hop varieties (EKG, Saaz and Styrian Goldings) and your favorite Belgian Ale strain (mine is 3787 at the moment).
I could just brew those over and over without getting bored for a long time.
I don't often get too out there, but I've brewed a few batches of Black Saison. Once, I secondaried in a corny keg with the dregs of two bottles of Orval and let it sour for 5 months. And once, I racked half a batch into a corny keg on top of some cherry puree. I was really happy with both of those batches.
Out there (for me anyway) ideas for the future:
A Belgian Dubbel brewed with homemade date syrup;
A rum/raisin Belgian Dubbel brewed with homemade raisin syrup and either using dark rum at packaging or a sugar product that produces a rummy flavor (it looks like MoreBeer still sells the dark candi sugar rocks, which I think would work); and
Black Champagne - a dark, highly carbonated beer that finishes dry and with a vinous character: all pilsner and refined sugar, a clean yet attenuative yeast (maybe a blend of 3711 and 1056 fermented cool?), Nelson Sauvin hops, and something to darken it (maybe Sinamar or blackprinz?).