Material components for spells are glossed over in the modern Dungeons and Dragons / Pathfinder collective. There are untold hundreds, or thousands, of spells, numerous classes with access to those spells, and all around no room for a complicated system which forces a caster to keep track of how much Bat Guano they've got on them. All things considered, I think the current system is adequate. For most spells with material components, those components can be found in the nondescript "component pouch." Those few spells with more costly components, which need to be purchased and tracked, are generally not those which a caster will find themselves casting very often. It's not perfect, but it works.
relegating material components to baubles picked up in any town robs us, GMs and Players alike, of a rich element in fantasy storytelling. So many classic tales of adventure revolve around recovering a rare item required for a wizard's spell. A spell which is, perhaps, the only thing which can wake the sleeping prince, or the best hope of finding the lair of the evil warmistress. Even when spell components are not the in the spotlight, it's almost a requirement for any story which features a wizard to include a list of strange and arcane items. Usually this list is recited whilst the wizard's apprentice runs about the laboratory, madly gathering "Eye of Newt" and "Wing of Bat."
Now, as mentioned above, I think the current system is adequate. There may be a better one, but I'm not concerned with finding it. What I do propose is a system which will allow material components to play a serious role in a game. One which will serve as a compromise between keeping track of each zombie knuckle, or squid tentacle; and throwing everything into a generic "Component Pouch." What if there were special material components which were not required to cast a spell, but could be added to a spell to enhance its effects. Like tossing a tablespoon of dill seed in the marinara sauce.
I'll demonstrate with an example from an upcoming game of mine. My players recently helped a town which was ravaged by fire. Turns out the eons-old red dragon king, Kolgoth'Ronnomaktar, has taken to flying around and breathing swathes of flame across the land in his old age. To prevent the same from happening again, the villages request that the party ask a kindly--but eccentric--old wizard to ward their village against fire. After a series of tests, the Wizard will happily comply, however, Kolgoth'Ronnomaktar's fire is particularly powerful, and normal wards are insufficient. In order to cast the necessary spell, the players will need to gather a branch from a tree which was struck by lightning, but did not catch fire.
This is a very specific example, but I think it shows how powerful and flavorful this element of fantasy has the potential to be. Below, I've compiled a list of unusual components and the effects which they might have when added to a spell. This list can be expanded to the limits of your imagination. However, the most important thing to remember is that none of these components should be easy to obtain. If a wizard can just drop into town and buy a bag of celestial's wing feathers, then all we're doing is buffing an already overpowered group of classes.
Ideally, casters either:
1) Embark on quests to gather these components for a specific purpose.
2) Receive them as treasure.
3) Harvest them when they happen to cross paths with the source during an adventure.
Items with which to enhance spells
[Color] Dragon's Tooth: Adds one damage dice to any damaging spell which uses the damage type of the Dragon's Breath weapon, and adds +1 to the saving throw or attack roll.
Example: Ezren is low on spells and needs to boost his Acid Splash to make it count. Since the spell does acid damage, Ezren uses the Black Dragon's Tooth he's been saving. He receives a +1 on the ranged touch attack required to deal damage with the spell, and since the spell deals 1d3 damage normally, it now deals 2d3 damage.
Example: The next day, Ezren is the last of his party standing and needs to clear a room filled with ghasts in a hurry. He decides it's time to use the Red Dragon's Tooth he found in a chest yesterday. Normally, his Fireball spell has a saving throw of DC: 18 and deals 7d6 damage. By consuming the red dragon's tooth, the spell has a save DC of 19, and deals 8d6 damage.
Handful of [Color] Dragon's Scales: Doubles the effectiveness of protection spells against the damage type of the Dragon's breath weapon.
Celestial Blood: Adds the [Evil] descriptor to any spell. Doubles the effectiveness of any offensive spell against good aligned creatures.
Demon Blood: Adds the [Chaos] and [Evil] descriptors to a spell. Doubles the effectiveness of a spell against Lawful or Good creatures. These bonuses stack.
Devil Blood: Adds the [Lawful] and [Evil] descriptors to a spell. Doubles the effectiveness of a spell against Chaotic or Good creatures. These bonuses stack.
Lock of hair from a King/Queen: Enchantment spells cast as two caster levels higher.
Shed Angel Feather: Adds the [Good] descriptor to any spell. Doubles the effectiveness of any offensive spell against evil aligned creatures.
Treant Branch: Allows a caster who has prepared "Summon Nature's Ally" to cast one level of the spell higher. This does not require a higher spell slot.
Vampire's Fang: Necromancy spells cast as two caster levels higher.
Balance could be improved on these. I have to admit I'm a little conflicted about whether I want to beef up the power on some of the low powered ones to make them more worth the time it would take to acquire them, or if I want to nerf the power down on some of the higher powered ones because casters are already overpowered.
Still, I think the above examples make the point.