I'm planning on brewing with my father who does not have the ability to brew lagers. We wanted to brew up ten gallons and split the batch. I have a big slurry of Wyeast Oktoberfest lager yeast that I want to use up, but he will be using a to-be-determined ale yeast. Any suggestions as to what style to brew? Recipe suggestions?

An Ofest certainly would work for what you intend. I've made a lot of PseudOfest using WY1007. The key is to be able to ferment fairly cool and cold condition it after fermentation. Can he do that?

I think so. Let's say he ferments at say 60 degrees. Bottles, then after the beer is carbonated, put the bottles in the fridge for cold conditioning? Would that work?

I was also wondering if there's something with a bit more hop character that might work. We have a huge crop of Cascades, EKG and fuggles at our disposal, but we don't HAVE to brew with them.

Well you could also try a California Common, although they generally aren't as hoppy.

Yeah, that plan should work.

None of the hops you list are traditionally lager hops, but that doesn't mean you can't do something with them. A Cascade pils kinda thing might be interesting. I've also seen Cascade used in CA common. although it isn't common.