Alright, so my two suggestions for an Outrider are Ranger and Hexblade
Here are my builds for a Halfling Outrider (assumes 5 levels then 10 levels of Outrider):
Ranger 5d8 HD, 6+ Skills, Good Fort and Ref saves
2nd Favored Enemy, Track, Wild Empathy, Rapid Shot, Endurance, Animal Companion, 0+bonus spells first level spells per day.
Pros: Animal Companion advances with Halfling outrider levels. Divine spells are nifty.
Feats: Mounted Combat(1) Mounted Archery(3)
Code:
Outrider Druid Possible
Level Feat Level[sup]1[/sup] Animal Companions
1 Precise Shot 3[sup]2[/sup] Boar, Dire Badger, Wolverine
2 3
3 4
4 Point Blank Shot 4
5 5
6 5
7 Improved Precise Shot 6[sup]3[/sup] Dire Wolverine
8 6
9 7
10 Far Shot or 7
Shot on the Run
[sup]1[/sup] For purposes of Animal Companion Abilities
[sup]2[/sup] If using a basic companion of a Riding Dog, Pony or Wolf, the companion gains
+2 HD, +2 natural armor +1 Str, 2 tricks and evasion
[sup]3[/sup] If using a basic companion of a Riding Dog, Pony or Wolf, the companion gains
+4 HD, +4 natural armor +2 Str, 3 tricks, evasion, and Devotion.
Note that not all large creature that big a deal (no pun intended) indoors ... for example, the Dire Wolverine should be fairly comfortable indoors. (At the same level you can have a normal wolverine with 2 bonus HD and a 10 ft burrow and climbs speed ... very versatile

)
Hexblade 5d10 HD, 2+ Skills, Good Will saves
Hexblade's Curse 2/day, Arcane Resistance (bonus vs spells and spell effect), Mettle, Summon Familiar, Bonus casting related feat, and 0+bonus spells first level arcane spells per day with 2 spells known. (Note: Hexblade can cast in light armor with no spell failure like a bard)
Pros: Mettle+Evasion mean great things on a successful save, and your familiar as a mount plus augment familiar is very nice. Your mount would have half your hps. Half of (5d10+10d8 plus 15*your con modifier) and an effective HD of 15 will prabably result in a fairly survivable mount.
Cons: Familiar abilities are weak.
Feats: Mounted Combat(1) Mounted Archery(3) Combat Casting(5)
Feats: Improved Familar -
Krenshar or
Worg would require 6 levels in Hexblade prior to taking Halfling Outrider. whoops. After that, Point Blank Shot at 9, Precise Shot at 12, Improved Precise Shot at 15.
Both versions are certainly very light on the feats but they have other abilities fighter builds can't have. The Hexblade version would do well as a Hex 3/Fighter 2 prior to entering the Outrider then continue on afterwards. (Finishing at Hex 5/Ftr 5/Out 10) Or, if you don't suffer multiclassing penalties, you can have fun with whatever combos you like
Some other nice feats: Improved Rapid Shot, Improved Favored Enemy, Ranged Disarm
1, Ranged Pin, Ranged Sunder, Zen Archery if your Dex sucks
1 The feat can be used with rays! "Cast your charms to disarm only!"
