My suggestions for skyrim:
1. Saddle bag, of course
2. I know horse back fighting is difficult to implement (so says the dev before oblivion was out), but we can amplify the charging damage a little bit. maybe different type of horses have different charging ability
3. Fast travel only allowed while on horse back. The reasoning being if you fast travel on foot you'll encounter dangerous situations so it's only safe to fast travel on horseback, which is faster
4. The horse needs to stop attacking the enemy. I always end up killing my horse while attacking the enemy just because he's in the damn way!
5. More realistic maneuvering animation for horses. see M&B. Oblivion horses are a joke. Remember the girl among the dev team before OB was out was talking about how she grew up with horseback riding and such? yea.
6. Make more unique (hero) horses and give them unique abilities. Such as, Mr Bucky is able to scare away all small wild animals so they won't come to hassle you while traveling.
other ideas?