You can find IDs by number at Minecraft Wiki. These prices are both what the server will buy and sell for.
/simbuy # ID to buy # of item matching the ID.
/simsell # ID to sell # of item matching the ID.
/price ID to check prices on item matching the ID.
Bone -- ID: 352, price: 15
Brick (block) -- ID: 45, price: 100
Cactus -- ID: 81, price: 1 (Cactus can't be sold right now, unfortunately. It has to do with the age of the cactus; I suppose you could cycle through the 16 varieties of cactus, and that could work.)
Chain Boots -- ID: 305, price: 10,000
Chain Chestplate -- ID: 303, price: 50,000
Chain Helmet -- ID: 302, price: 10,000
Chain Leggings -- ID: 304, price: 25,000
Clay (block) -- ID: 82, price: 40
Cobblestone -- ID: 4, price: 1
Diamond Block -- ID: 57, price: 4500
Diamond -- ID: 264, price: 500
Dirt -- ID: 3, price: 1
Dye, Bone Meal -- ID: 351 15, price: 15
Dye, Cactus Green -- ID: 351 2, price: 15
Dye, Cocoa Beans -- ID: 351 3, price: 15
Dye, Cyan Dye -- ID: 351 6, price: 15
Dye, Dandelion Yellow -- ID: 351 11, price: 15
Dye, Gray Dye -- ID: 351 8, price: 15
Dye, Ink Sac -- ID: 351 0, price: 15
Dye, Lapis Lazuli -- ID: 351 4, price: 15
Dye, Light Blue Dye -- ID: 351 12, price: 15
Dye, Light Gray Dye -- ID: 351 7, price: 15
Dye, Lime Dye -- ID: 351 10, price: 15
Dye, Magenta Dye -- ID: 351 13, price: 15
Dye, Orange Dye -- ID: 351 14, price: 15
Dye, Pink Dye -- ID: 351 9, price: 15
Dye, Purple Dye -- ID: 351 5, price: 15
Dye, Rose Red -- ID: 351 1, price: 15
Feather -- ID: 288, price: 10
Glass -- ID: 20, price: 5
Glowstone Block -- ID: 89, price: 100
Gold Block -- ID: 41, price: 4500
Gold Ingot -- ID: 266, price: 500
Gold Ore -- ID 14, price: 100
Gravel -- ID: 14, price: 1
Grass -- ID: 2, price: 100 (This block is dirt, but it has grass pre-loaded on it. You can use this to jump-start grass growth on dirt, and, while I haven't tried it, I suspect you can use this to grow grass in the Nether.)
Gunpowder -- ID: 289, price: 10
Iron Block -- ID: 42, price: 2250
Iron Ingot -- ID: 265, price: 250
Iron Ore -- ID: 15, price: 50
Lapis Lazuli Block -- ID: 22, price: 135
Moss Stone -- ID: 48, price: 150
Netherrack -- ID: 87, price: 1
Obsidian -- ID: 49, price: 200
Pumpkin -- ID: 86, price: 10,000
Redstone -- ID: 331, price: 5
Redstone Torch -- ID: 76, price: 6
Saddle -- ID: 329, price: 1500
Sand -- ID: 12, price: 1
Sandstone -- ID: 24, price: 4
Seeds -- ID: 295, price: 50
Slimeball -- ID: 341, price: 1,000 (This has no use in game right now, so don't bother buying for the moment. Slimes drop them, so they could be worth your time to kill, though!)
Soul Sand -- ID: 88, price: 10
Stick -- ID: 280, price: 1
Stone -- ID: 1, price: 5
String -- ID: 287, price: 15
Sugar Cane -- ID: 338, price: 1
Torch -- ID: 50, price: 5
Wood, light -- ID: 17 2, price: 8
Wood, dark -- ID: 17 1, price: 8
Wood, normal -- ID: 17 0, price: 8
Wooden Plank -- ID: 5, price: 2
