In second edition D&D, there is a little known class called the Sha'ir, which was a sort of wizard from Al'Qadim that had a sort of alternative model for obtaining spells. Instead of memorizing them, the wizard would send his gen, or little genie, off to fetch the spell, and the genie would return with the spell a round or two later. The benefit here being that the sha'ir was not constrained so much by spell level. The gen would take longer to fetch a spell, the more above the wizard's grade it was, though.
Eventually, there was a Complete Sha'ir Handbook, which was part of the first class-based splatbooks to be published for d&d. For all I know, it was the first rpg-related splatbook series ever. Anyway, it was amazing. Back in 2e there were these things called kits, that were basically a way of customizing a generic class into something more specific and interesting. Like, a thief would take a jackal kit and start stealing peoples' spells, but at great cost to his other abilities. Not that 2e thieves really had abilities, but you get the idea.
In the Complate Sha'ir Handbook, there were probably fifteen or twenty crazy, zany, downright whackadoo kits for sha'irs. Whoever wrote it must have figured "hey, it's not like the sha'ir has any semblance of balance or functionality to begin with, let's just see how much crazy crap we can come up with." And boy, did he ever succeed.
Sticking out in my head are the mathemagician, the astrologer (who would hang spells on different constellations), the spell slayer (holy wizard-assassins), and the clockwork mage. Especially the clockwork mage. That fucker basically assembled clockpunk robots from scratch, with a list of parts and power sources. You basically spent all your time (and gold) on building crazy robots. It was almost freeform in a lot of ways. And if it died you were out hundreds or thousands of GP. But get a player with a lot of artistic talent or zest for creativity in that class, and you'd end up with half-deer half-lobster mechanical beasties that fired lightning bolts out of their horns.
Sad to say, but in the 2.5 editions since then, nothing has really topped this class for cool factor, and no splatbook has topped the Complete Sha'ir for really creative shit. A lot of the splatbooks have just been updating older, popular options, I guess. But that's no excuse. It's possible that you just can't do as much fun stuff when balance is so paramount, as it has nominally been in 3e and 4e. But where's my fucking clockwork class? Where's my inventor? Where is my balanced system where someone actually builds something? How about a golem construction pet class? Or a wizard biologist that designs his own homunculi? This shit should be easier now that wealth is actually handed out at a more or less set pace. There's homebrew crap on the internet, but my choice of the term "crap" is non-accidental in this case.
All I want is some fucking clockwork.