If you're an Excel junkie (or just want to be one) take a look at
Mr. Excel.
Mr. Excel has a daily videocast on Excel topics and the topics seem to run the table from simple to complex. Hint, there's more than 600 videos so far. I don't have a nice clean transition about how this affects Dynamics GP but lets face it an awful lot of GP user are heavy Excel users and the connections between the two are only getting stronger.