Bukkit

This is a list of all currently available Microblocks (it may not be updated that often):

apple
arrowdown
arrowleft
arrowright
arrowup
enderchest
monitor
blaze
blookshelf
ice
ironchest
furnace
spawner
qcube
cactus
cake
camera
cavespider
horse
cherry
chest
chicken
clock
coconut
companioncube
cow
derpysnow
diamondblock
diamondore
glowstone
beachball
dicewhite
dicered
diceblack
dirt
dispenser
emeraldore
enderdragon
enderman
exclamation
golem
grass
haybale
headlight
herobrine
ironblock
witch
jukebox
lampon (lamp on)
lavaslime
lemon
lime
machine
mossycobblestone
mushroomcow
netherrack
notexture
oaklog2
oaklog
obsidian
ocelot
orange
eyeofender
pigzombie
pig
piston
podzol
popcorn
present
pumpkinface
pumpkin
quartzblock
question
radio
redsand
redstoneore
rubixcube
sand
sheep
slime
speaker
spider
sponge
squid
stickypiston
stone
taco
tnt2
tnt
toaster
toiletpaper
tv
villager
ghast
oakplanks
gamecube
redstoneblock
tv2
troll
eye
parrot
pokeball
cookie
workbench
orangewool
stonebrick
swskeleton (sideways skeleton)
swzombie (sideways zombie)
goldbock
fox
potato
leaves2
cobblestone
water
noteblock
brick

(and more are coming!)