Going to write these 5 tasks on the assumption you are going to be using
http://ftbwiki.org/Hardcore_Questing_Mode or something similar, so that the tasks can be multi part and easily detected. By going with this assumption you can add in all the other ones people come up with in this thread together.
Thaumcraft.
1. Getting Started: You've heard of the amazing power that thaumaturgists have in the world. You are determined to have this for yourself.
A. Requirements Consume: 1 iron capped wooden wand, Have: 1 Bookcase Reward: 1 Iron capped wooden wand with 25 of each aspect.
B. Requirements Have: Thaumonomicon
2. Scan All the THINGS: A wand and a book will not get you very far when the book is almost empty. Seems the ancient thaumaturgists are not going to simply let you have the secrets, you are going to have to research them yourself.
A. Requirements Have: Thaumometer Reward: 32 Knowledge Fragments
B. Requirements Have: Research. Reward: Crucible research, alchemy, Nitor
3. Batches of Brewing: With the notes I have given you a start can be made into the lore of the thaumaturgists. This is just the first taste, for anything more you will need to do the research yourself.
A. I require for you to make me some nitor to prove yourself to me. You'll want to use the first one to make the crucible more efficent. Requirements: Consume: 8 Nitor
4. Pulling Apart & Putting Together: Once you have completed much of your research come back here and talk to me again.
A. Pulling Apart : First look into the Alchemical Furnace. Bring me a Vial of each of the 6 Primal aspects. Consume: 1 Vial of each primal. Reward 1 Void Warded Jar of each Primal Aspect.
B. Putting Together: Have: Infusion Matrix
C. Masterwork Project: Before you can end your aprenticeship with me, you must show your mastery. I require you to produce a set of runic armor, so that you will not shame me by dying. Have : Runic Armor
5. Taking on a Student: Perhaps you are ready for your own student, perhaps you only think so, you might want to start out slow.
A: Requirement: 1 advanced golem ... At least this one will listen to you.