I actually just got off the phone with a Mckinsey HR yesterday. Discovery will be up and accepting apps around January time. Other than that, there doesn't seem to be any spring stuff.
Your best bet would be to apply to small consultancies and ask for work experience (something I've done). You can then use this as a springboard to summer interviews. Also get any w/e at blue-chip firms (if you can). This is viewed very favourably.
BAIN, Accenture and others run summer programmes as well, but these are strictly for penultimate year students. I might risk a speculative application for Accenture, though.
As for why I would choose BAIN: it is a top tier consultancy and it seems to have a great work culture (dead important when you consider the hours you'll put in). MOW also looks good because it's new: there are great opps to get quick promotions; inflated salaries; apparently they also stick to a sub 55hr week.
Accenture is okay but viewed as easier to get into and less strategy-focused than the others - which need not be a bad thing. McKinsey is viewed as the industry leader and CEO factory; get this on your CV and you're well-placed for industry.
Kentish: If you'd like to know more, I'm editing a I&F journal, which is doing an issue focused on MC ... I'll email you it when it's finished, if you like.