Although the melee druid can be a potent fighter, the missile-oriented druid is also an effective choice -- mostly because the druid's animal companion is the best mount in the game.
The druid who uses a double weapon in combat, such as a Shillelagh-enhanced staff, gains the most benefit by attacking multiple times per round. But that requires a full-round action. Any round the staff-wielding druid spends taking standard actions, or moving more than five feet, is a round in which she is not fighting optimally.
But a druid using ranged weapons can take a full attack even while her mount is moving! If her mount makes a standard move, the mounted druid can make a full missile attack with no penalty. If the druid directs her mount to make a double move, she can take a full attack, but at -4 to attack. If her mount is flat out running, she can still make a full attack, but at -8. The mounted archery feat cuts those penalties in half, to -2 and -4.
But what mount? Horses just won't do -- not maneuverable enough. A good mount is big enough to ride, but not too big for caves, dungeons, and buildings. But for medium size non-aquatic druids, there is no other option than a horse (or a camel, LOL!). Which suggests the ideal solution for the missile-combat druid: playing a small-size character.
A first level small druid can ride a nimble medium-size mount, like a riding dog or a wolf. Canines fit just fine in dungeons, buildings, and other small spaces. For a medium size druid, an equivalent large size nimble mount is not available until level 8: the dire wolf, the dire wolverine, or perhaps the deinonychus. At level 4, the small druid can even take to the air, with a dire bat companion.
There are lots of other advantages to playing a small druid as well. The +1 size bonus on attacks and AC is a solid plus. Playing a halfling also offers a +1 racial bonus on some missile weapons, as well as a +2 Dexterity. Those three advantages put the halfling druid at +3 to hit over an equivalent human.
Another small race to consider is goblin, if your DM allows it. Goblins gain a +4 racial bonus on Ride checks, and gain a +2 Dexterity bonus as well. That +4 on Ride checks is pretty sweet for a character who never dismounts.
But what missile weapons are the best for our druid? In the 3.0 version of the rules, druids were allowed to use only druidic weapons. However, under the 3.5 rules, druids are restricted by armor, but can use any weapon at all! For the melee druid, it doesn't really matter, since the Shillelagh-enhanced staff is better than any other melee weapon. For the missle-using druid, it opens up the option of using bows and arrows. But that's a trap! Archery is not usually the best choice for our missile-oriented druid.
The whole idea is to maximize full attacks! With bow and arrow, the Rapid Shot feat offers two attacks per round while BAB is +0 to +5. At a +6 BAB, that increases to three attacks per round, and at +11 BAB, four attacks. But you can use Two-Weapon Fighting with thrown weapons, throwing with both hands at once. With Improved and Greater Two-Weapon Fighting, that means four attacks per round at +6 BAB and six attacks per round at +11 BAB.
Don't forget that halflings get that +1 racial bonus with thrown weapons, another reason to disdain bows.
If you do want to play that mounted halfling druid who throws weapons with both hands, what else do you need? You absolutely must have Quickdraw, because otherwise drawing a weapon is a move action, putting the kibosh on your full-attack plans. You also really need a high Dexterity, since the Two-Weapon Fighting feat chain requires it. That high Dex also helps with ranged attacks, of course. You want to max out your Ride and Handle Animal skills. Other useful feats include Mounted Combat and Mounted Archery, Animal Affinity, Skill Focus (Ride), Point Blank Shot, Far Shot (because thrown weapons have poor ranges), Precise Shot (for throwing into melee), and, later on, Improved Two Weapon Fighting and Greater Two-Weapon Fighting. That's eleven feats! How can a poor druid ever get that many feats? He can't, unless he multiclasses!
Let's multiclass our throwing druid. The two choices are fighter (more feats) and ranger (Two-Weapon Fighting, levels stack with druid for animal companion and wild empathy, more skills). The druid/fighter can start true to concept at first level as a fighter with Quickdraw, Two-Weapon fighting, maxed out Ride and Handle Animal, and a purchased riding dog; at second level, taking a level of druid, she gains a wolf or riding dog companion. The druid/ranger has to be more patient, waiting until druid1/ranger2 for Two-Weapon Fighting. For those who are willing to sacrifice spell-casting, the druid/ranger/fighter is a good option as well -- great saves, great BAB, excellent companion, lots of feats. As a halfling (or gnome or goblin), though, keep all your classes near the same level, to avoid any multiclassing xp penalties.
So what weapons, for our throwing druid? When throwing with the off-hand, only daggers, darts, and shuriken count as light weapons -- darts are the best of those. With the main hand, though, the choices are greater. At low levels, the best choice may be a surprise: alchemist's fire! A flask does 2d6 damage (over two rounds), as good as a human's greatsword! At higher levels, returning magic throwing weapons that deal bonus dice of damage are pretty sweet -- the +1 holy returning trident is a nice choice, but it's hard to afford four (at +6 BAB) or six (at +11 BAB) returning magic weapons! If you end up with weapon focus and weapon specialization, it makes sense to throw specialized darts with both hands.
But our ranged fighter is also a spell caster! What spells work best? Cure spells are always welcome. Speak with Animals lets you communicate more clearly with your companion, if need be. Entangling foes -- and then firing at them -- is fun (tanglefoot bags work well for that, too). Longstrider is great because you can share it with your companion (for that matter, sharing cures when both you and your companion are wounded is a great trick, if your DM lets you do it). Spider Climb is another great spell for your companion -- firing at enemies from a ceiling is great fun (so is Air Walk at higher levels). Buffs like Magic Fang, Greater Magic Fang, Barkskin, Cat's Grace, and Resist/Protection from Energy are often useful.
Well, it's a pretty specific character build I've described here -- the halfling druid/fighter/ranger who throws weapons with both hands while mounted. But done right, this concept has great strengths, versatility, and the virtue of being unusual.