The (prestige) class that HASN'T been crafted yet ...

[Jolly Giant]

I've made a couple of PrCs for my homebrew; maybe not quite arch-typical, but themes I couldn't find in any other PrC:

Sumo-wrestler

mage/druid combo, that specializes on animals; combines animal companions and familiar into multiple familiars

Blackguard-esque archer PrC