A large amount of my post is restating what has been stated elsewhere, but I'd like to get it into one place, add a few of my own suggestions, and mind force it.
Hoe - Aids in the harvesting of crops that grow underground, such as carrots, onions, and hopefully some time potatoes. Also increases the speed of planting.
Shovel - Increases the speed of digging dirt, clay, and sand.
Scythe - Aids in the harvesting of crops that are harvested by chopping them down, such as flax and wheat.
Metal Axe - Because the world doesn't cut all its trees down with stone axes. (even though I have to agree, the stone axe is the shit)
Pitch Fork - While equipped it automatically picks up straw or flax left sitting on the ground that you walk over. Has an inventory of 16 spaces. Right clicking a container while the pitch fork has something in its inventory will fill the container with what the pitch fork picked up. Rick clicking the ground or de-equipping the pitch fork will cause it to drop what it contains on the ground. Alternatively, collected straw and flax goes into your inventory.
Seed Bag - This has been talked to death, but I offer yet another possibility: Has an internal inventory of 16 (for 4x4 farm plots, which seem the most popular.) Right clicking it will open a new inventory window similar to opening a basket. Taking the seed bag and right clicking the ground causes all the seeds to be planted in accordance to where they are in the inventory. Also, some way of sorting quality besides by hand would be really, really nice.