The only "proper" synth in the studio right now is a Roland Juno 6, which is a polyphonic analog synth. Sometimes that's been used on Califone sessions. Couldn't really point to any song in particular. There's also the mighty Sherman Filterbank, which is a dual oscillator analog synth. No keys on that, just some knobs. It's a hyped up, glorified EQ sorta thing that takes pre-recorded sounds and totally messes them up. If it sounds a bit like a drum, but made out of some alien material, and it has a strange decay to the sound, it's probably been through the Filterbank at some point.
Nord makes great instruments. The Nord Electro comes as close as I've heard to accurately imitating classic analog keyboards like the Rhodes 73, Wurlitzer 200, and Hammond tone wheel organs. We have original versions of those in the studio so we don't need the fake sounds. Last time I counted there were 15 different keyboard instruments in the studio, all of them original oldies. If you hear a Hammond organ sound on a Califone track, it's a REAL Hammond.
I've heard the Nord Leads are cool, but I suspect that they're more useful if you know how to play keys. Mostly they make cool, controlable noises, that a skilled user could probably make sound a little like strings or horns, or maybe even exploding expectations. You want snyth examples, just listen to some Pink Floyd or Yes...
"how was that take?"
"it sucked...c'mon in..."