For the farmers in a couple of custom builds, I've been having them give you pumpkin and melon SEEDS, for gold nuggets, instead of them wanting pumpkins or melon blocks for whatever it was they would give you (can't remember right now). Then once you get your pumpkins and melons growing, you can trade them pumpkins for pumpkin pies or melon slices for cookies (or anything else you want to change it to).
Also, you can give even the adult villagers custom names and change their professions and/or careers, so if you have, for instance, a whole troop of librarians in a village you find, just load up the world in NBT Explorer and fix them up so you have all of the necessary ones to do even the regular trading system, which eventually will give you pretty much everything you need in the game.
Anyway...lots of fun, and VERY easy, once you know what to look for.
It's definitely a WHOLE lot easier than doing the same thing with command blocks!!!
