For this week's addon, I thought I would share one that is built around a macro that we've hinted at over at Macro Anatomy. This addon has been abandoned by the author, but there is a patch available that will update it to work with 2.4. (Although I am using the "unpatched" version just fine.)
GoGoMount will pick the most appropriate mount for you based on given conditions. If you can use a flying mount, it will summon your flyer, otherwise it will randomly select from your ground mounts. (This includes summoned mounts for Paladins and Warlocks.) If you have multiple flying mounts, it will randomly select one of these as well.
It supports Druid travel forms and Ghost Wolf for Shamans as well. So, in less words; this addon is your one-stop mounting shop.