I have a druid/druid duo that just made it to 60, Feral/Restorative combo. This combo turned out to be quite fun for me, so I stuck with it. I'm an alt-tabber running 2 accounts on one computer.

What I like about it.....
-ability to heal/rez from both toons
-either can tank (bear) at any time (nice to pull out 2 tanks when the occasion arises)
-both can dps (tiger) if you want to rip through mobs
-both have early 40% run speed....makes for great quick transport option IN UNISON (try to have a druid with 40% run speed and the other toon without - bummer)
-differences in talents makes them shine in their own ways regardless of being the same class