Multiple MIN queries

Can anyone help?

I have a a dataset where column A is a list of days and colum B is a list of times, e.g.

Col A Col B
01.01.2011 09.15
01.01.2011 11.33
01.01.2011 10.27
02.01.2011 07.31
02.01.2011 14.01
03.01.2011 12.00
03.01.2011 09.54

etc...

I'm looking for a formula that would return the min value in column B for EACH day. Any ideas?

Thanks

Steve