Druid//Ranger grants you all Druid goodness with extra combat awesomesauce. Talk to your DM about if having the Animal Companion ability twice, but at different levels, means you get 2 critters.
Cleric//Paladin? Simple, classy, serious Omph.
Sorcerer//Warlock? Choose a lot of battlefield control stuff and some buff spells. when you hit level 6, aid your allies while remaining invisible.
Can't ignore Factotum//Wizard as a utility combo. A better skillmonkey than a Rogue, and the spells that make you Batman. Use IP if you want to hit somebody a few times in an encounter, but you've honestly got better things to do.
It doesn't have spellcasting, but to emphasize Support, some combat, and nifty abilities, how about a
Marshal//Dragon Shaman?
It is by no means optimized, but everyone will become more powerful simply by standing near you.
If you can get your hands on Miniatures Handbook, Healer//Warmage could be fun to play. a little MAD, but you get to blow them up, and put them back together!
I don't know how many levels you guys plan to go, so I'm trying to think of builds that are useful off the bat.