I always wanted to play a Malconvoker, but my group would not have been comfortable with it. It's a class whose core conceit is that they summon demons and make pacts with them that trick the demons into serving good causes. The demons are convinced that the Malconvoker is a traditional evil cultist or self-serving wizard, but it turns out all the favours they grant them are twisted to good ends and all the prices they demand get paid in unexpected ways that turn out to be not as costly as intended.

The key stat is charisma and bluff is the most vital of skills, of course.

I have dreamt of having a druid with all levels of Warshaper and at least 1 level of Master of Many Forms. The possibility of always being in wild shape with all of the benefits of Warshaper sounds so much fun.

Jade Phoenix Mage was pretty cool. The capstone ability was that you literally explode, dealing a huge amount of damage to everything nearby and literally vaporising yourself. Then you reform on the same spot 1d6 rounds later completely healed of damage and most conditions, with all your gear.

The Chameleon and the Thousand faces were some of my favourites in concept because of their flexibility, though I never had a chance to play them. Gish builds in general were a lot of fun. There also was a Sand mage in a desert theme manual that was very interesting.