The TaxProf Blog published its top 10 for 2005. Their top ten includes the Kanter/Ballard Tax Court case, the telecommuter tax case, and the federal tax reform initiative. There are other items on the list, of course. I could quibble with some of the items that are left out, but the collective brainpower on the TaxProf blog far exceeds my own (especially at 7:00am).
You can find the list here.