Here is my list of Buildable blocks and items. I'll be updating it as more come up and/or they are added to the game. Feel free to suggest some below and I'll add them to the list.

New items will be marked with a NEW tag in brackets behind their name. A new item was added in the last edit of this post.

• Circle of Protection [NEW] - This circle, drawn with chalk, can be used to contain a single spell. A spell that would create an AOE effect will not extend beyond the Circle of Protection. Creatures summoned in the Circle of Protection may not exit it. Great for training or creating a moving decoration.
• Floaters [NEW] - Floaters are blocks that may be placed in the air. They move slightly up and down but otherwise stay stationary. Floaters may be pushed if a player walks into them or hits them with a spell that creates a force. Floaters have high friction.
• Crafting Tables [NEW] - Used to make potions, armor, weapons, books, and more.
• Flowers,Mushrooms [NEW] - Someone, somewhere, is going to want to plant a garden. Wildflowers which can be harvested and transplanted somewhere else would be cool. Wild mushrooms which can also be planted to make mushroom farms, crushed into potions, or eaten to grant special powers.
• Chandelier [NEW] - This fixture hangs down with four sides that can have torches, decorative shields etc hung on them.
• Rope [NEW] - Use this to hang Chandeliers, climb out of tunnels, or scale walls. Can be attached to a grappling hook to allow throwing and provide a wall climbing utility.
• Target/Bullseye - Used for practicing magical and ranged attacks (arrows/crossbows etc) accuracy.
• Mana Spring - When standing in a Mana Spring the user regenerates mana at an increased rate.
• Fountain of Health - When standing in a Fountain of Health the user regenerates health at an increased rate.
• Gate - These massive doors must be opened with an electric trigger or lever. Great at keeping your castle safe.
• Orb of Light - This magical orb may be summoned in the air. It provides constant, unwavering light that is stronger than a torches. Additionally Orb's of Light are not put out by water. Orb's may be attacked and destroyed however.
• Ladder
• Window/Glass Block
• Double Door's
• Conveyor Belt - Faces the direction the player was facing (NSEW not Up/Down). Will move blocks/people/npc's 1 square above it in the direction it faces.
• Piston - Faces the direction the player was facing (NSEWUD). When activated will move the block 1 square infront of it (based on direction) 1 square in that direction.
• Lava
• Water
• Slime - Swimming in slime is harder than water and it eats through armor.
• Electrical Wiring - Minecraft Redstone or something original. I don't care but this is needed to activate traps etc.
• Trap Door - When activated the door opens, causing whoever is ontop of it to fall.
• Pressure Pad - Used to activate a trap when someone steps on the plate.
• Lever - Used to activate a trap by pulling the lever (levers are toggled on/off).
• Button - Used to activate a trap by pushing the button (buttons are only on/off for 1 activation)
• Trip Wire - Used to activate a trap when a player or NPC crossed the Tripped squares (toggle trap on/off).
• Chest - Store armor and resources here.
• Sign - Say something nice
• Bulletin Board - Bigger version of the sign. Allows players to create quests such as: collect 200 granite or kill 20 goblins or kill Mardok. They can assign their own rewards etc. Other players may than go and accept the quest. The sign would show how many players had already accepted the quest and how many rewards their could be. For example their may only be 5 rewards available for collecting the granite. The 6th person would be out of luck and would simply have 200 granite. Think of it as trading but not instantly.
• Spike - Place these in walls, anyone that hits them takes damage. Anyone that gets stuck in them dies.
• Bed - Sleep...
• Chair - Why are you standing all the time, sit down, have a drink.
• Stove - cook your food in style.
• Furnace - Purify the metal you mine so you can use it for crafting.
• Anvil - Make yourself something nice out of all that hard work.
• Trees - Players can plant saplings, they grow over time into full trees which drop more saplings. Perhaps introduce an NPC such as a wood nymph or something that plants saplings in uninhabited areas so trees never just disappear.
• Cannon - Made from steel the cannon can break your friends toys!
• Motion Sensor - When a player comes anywhere near a motion sensor it activates until the player leaves proximity.
• Explosives - Mine more efficiently or lay siege to your enemies.
• Map - Placed on top of another block. The map displays the surrounding area.
• Compass - Placed on top of another block. The compass displays the direction toward North.
• Ballista - Similar to cannon except fires faster and has a longer range. Ballista bolts do not destroy blocks though.
• Cage - Used to keep all those unfriendly guard trolls.
• Drawbridge - A 2x2 bridge that can be raised with electricity or lowered from the lack of it. Useful for castles.
• Picture - Jazz up your room with a random picture.
• Bookshelf - Keep books on it.
• Fireplace - Keep a fire here. Great for directional lighting.
• Ice Block - Frictionless block. The ultimate puzzle block.
• Drop Block - Floats in the air until someone stands on it. Then it falls down. When no one is on the block it rises back to it's original position. Fake bridge anyone?
• Treasure Block - Looks like a normal block but can be opened to store items. Used for storing secret treasure.
• Shocker - When charged with electricity it emits a burst a few meters around it. Damaging all in the area.
• Floodgate - Can be used like a damn.
• Flag - Mark your territory with pride, waves your flags high.
• Corn, Wheat etc - Because someone is going to want to make a farm. The refined materials can make bread, cake, corn, popcorn etc which will heal health, magic points or something.
• Fence - Block of your territory without scaring away the neighbors.
• Bear Trap - When stepped on the trap does damage and slows the effected person. After activation a bear trap must be reset. They should be hidden as spotted ones may be disarmed and stolen.
  

That is all, for now, if you want me to add something to this list, just ask (↓ comment ↓).

great! I hope to add most of them as objects (new type of action)