Since most of my emails are B2B I jumped on the bulletproof button bandwagon to get calls to action displaying perfectly in outlook clients.

Unfortunately I learned the hard way that bulletproof buttons aren't bulletproof when your ESP's platform messes about the VML and mucks up the code. Shame on you Campaign Master. To be fair to them they do now have a new improved platform, but my organisation is slow to upgrade to the new platform.

In light of the above, what's your favourite (alternative) methods for creating great calls to action?