I'm working on a guild in which I'd like to be able to assign members certain tasks in the form of quests. For example, to the skinners: Collect x number of light leather; to the miner: Mine x number of copper ore and smelt it; to everyone: Kill x number of Bloodsail Pirates; etc. I plan to use another addon to give members reputation, and posibilities for rank increases as rewards for these guild quests. Is there an addon or could someone please develop one, so that a guildmaster could set up quests for their guild members to complete?

You might want to look around at the RP related addons. I believe there are some that, if both parties have the addon, allow you to create simple quests and give them out.

Thank you, I'll look around in that section then. Anyone have any specific names I should look for?

if you find one, post the name of it here so others can benefit from the knowledge as well :)

RPHelper maybe? I forget since I don't really take note of the role play related addons.

RPHelper is an addon that I use, it takes certain events (theres a long list of them) and gives your character a chance to automatically say or do something in response to that event.
Anyone else have any suggestions? Right now I'm just writing the quest in the guild info tab, but there's only so much room there to write, so if I make 1 or 2 more quests, I'll be out of room to type.

Have you tried Group Calendar?

This is best in that you can schedule certain events and they can check wether or not they choose to attend. Unfortunately, you wmight want to assign a guild officer to moderate these to keep people honest. If you are requiring them to bring specific items to the guild then, it should be easy to track as they can enter them into the guild bank. Group Calendar is also good for scheduling meetings, instances, raids, etc.

I have made it a standard in my guild. Once someone joins, they will be an initiate until they have Teamspeak (to be able to talk and hear), Group Calendar and be at least level 30.

That's all I can think of that might be of value. The only other thing I can think of is maybe contacting and paying a developer of add ons to make a specific mod for you. If you do this - I would certainly raise more than an eyebrow :) !!!