When do most people suggest putting down an apartment deposit by?

Depends on when your move date is and how far in advance the landlord wants it/has a vacancy.

I guess my question is in general. I'd be moving sometime in August for school. I'm still choosing between two schools and am worried that by the time I decide, my housing options will be limited.

What I'm finding is that the apartments don't even know what vacancies they'll have until a month (45-60 days max) in advance.

Alright! Thanks : )

No prob. At first I thought you were asking for a specific date and I was all 'pfft, how would we know?!'

It depends where. Some places, especially those with many students in the area, fill up now. However, there are usually apartments opening every so often, so it shouldn't be a huge problem.

It really depends. I've been places where the good apartments for next year start to go in October, and I've been places where you couldn't sign a lease a month ahead of time if you tried.