Of course, now I want more. The obvious place to look is the Millenaire mod, which adds all kinds of new stuff and items. But I'm always a bit wary of big, intrusive mods - I like my Minecraft fairly vanilla.
So this is the villager mod I actually want and may code up one of these days:
First, the mod slightly lowers prices, by about 20-50%, which still leaves the villagers with plenty of profit margin, but should make trading a more attractive alternate prospect for actually getting items you want. (Rather than just accumulating emeralds as a kind of score, which is what I'm doing right now.)
Second, it introduces some more villager types to give a wider range of trading options. They are:
Baker (common)
- Buys wheat, sugar, milk buckets and cocoa beans
- Sells bread, cake, cookies
Fisherman (fairly common)
- Sells all kinds of fish (of which there will be more in 1.7) and ink sacs
Carpenter (rare)
- Buys raw wood blocks
- Sells wooden items like stairs, trapdoors, chests, etc.
Dyer (rare)
- Buys white wool and dyes
- Sells colored wool and carpets
Miner (rare)
- Buys pickaxes, shovels, torches, TNT
- Sells coal, iron, gold, redstone and diamonds
Alchemist (very rare)
- Buys glass bottles and potion ingredients
- Sells potions
Engineer (very rare)
- Buys redstone, wood planks, iron and slime balls
- Sells dispensers, droppers, hoppers, daylight sensors, repeaters, comparators, redstone torches, pistons (sticky and not), lamps, rails of all kinds
That's pretty much it. Optional nice things would include making the prices of things dependent on the biome the village is in (wood in a desert is more expensive, etc.) and changing the measure of village size to be additionally restricted by number of beds and inside area.