Any particular Object models that you were interested in (Excel Object Model, Access Object Model, etc) or all of them? I had a copy of Excel 2003 VBA from Wrox that was pretty decent, they have updated it for Excel 2007 (although I don't believe that there would be a difference between the 2003 and 2007 versions as extending VBA was pulled years ago and there was a push to move to VSTO).
As a general VBA reference, you'd be best to pick up a good VB6 resource, since if I recall correctly, VBA is a subset of the VB6 language. Something like Professional Visual Basic 6 Programmers Reference would be good.
EDIT:
The MSDN Visual Basic for Applications page looks like a good starting point for resources. Here are the Language References
