Well, for quick mounting/dismounting...
A DC 20 Ride check lets you mount/dismount a mount as a free action, as long as you still have a Move action for the round.
So someone with a +19 Ride modifier can always do it, as long as they have a move action left to use.
Which brings me to another fun find: the Halfling Outrider PrC can grant an infinite number of attacks, as long as you have a single move action left unused and you have at least 5 levels in the class.
1. You ride up next to your poor target. Wait a round, or point out that you haven't used a Move action yet.
2. You make a DC 20 Ride check to dismount into an adjacent square. Then, since your enemy is within your reach (you rode up to the bastard), you get a free melee attack with a +2 to hit (but, unfortunately, a -2 to AC.)
3. Then, make a DC 20 Ride check to get back on your mount.
4. Repeat 2 and 3 until your opponent is made of fine, fine paste.
Ta da!