Unless I've missed it (which, from a bit of web searching, seems to be unlikely) the date hasn't been announced yet.
Last year the date of the Budget was announced on 12th February. The absence of any similar announcement this year has led to speculation that there will be no Budget statement prior to the General Election.
The pre budget report was deliverd on 9th December 2009 - and a budget can't be held until 3 months after that date - so in theory it could be any time after 9th March.
There has been plenty of talk about a 'springtime' budget together with a May election - so late March or maybe April (like last years) would be favourite.
Unlike Chris, I believe that there will be a budget before the election.