My university course gives me a 3rd year placement, and yes the economy is bad, but the stockmarket ticks on.
Wouldn't go big 4 accountancy for a placement - I think Deloitte do one but you won't get any decent exposure unless you plan to follow the career up post uni.
Personally I did my placement year at a small company and got involved in everything from Accounts to HR (including taking notes in a meeting where someone got fired) to Operations to Marketing. Others who got into big companies ended up as a glorified office junior.
Also right now smaller companies will probably be shedding dead weight staff so there will be more opportunities for you to get completely involved in every aspect of the business
It's a great opportunity to put something on your CV that a lot of graduates won't have, it could be vital in the current climate where (assuming you've got 2 and a half years left) graduates will be competing with people who have a few years ecperience and are rebuilding their working life