Minecraft has a lot of old blocks, but it also has some interesting ones
This list below is every weird looking block from version 1.6.1
All of the blocks on this list were found by xzas and qwertnoah.
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Wooden Door (#64) Bottom half of a oak door.
Sign (#63) Works as a sign but you can't write on it and the texture in the hotbar looks interesting.
Crops (#59) Texture for wheat in its first stage of growing.
Redstone Dust (#55) Redstone texture but white.
Nether Wart (#115) Nether wart in its first stage of growing.
Bed (#26) The bottom half of a bed.
Fire (#51) Fire when its placed down.
tile.flowerPot.name (#140) The same as a normal flower pot just a different name and texture.
Tripwire (#132) The texture for tripwire when its placed on the floor.
tile.null.name (#34) The texture of the top of a piston
Shrub (#31:0) Dead bush variant that can sustain on grass.
Cocoa (#127) One of the growing stages of cocoa.
Water (#9) Water texture.
Lava (#11) Lava texture.
Iron Door (#71) Bottom half of a iron door.
Sugar Cane (#83) Texture of a sugar cane.
Portal (#90) Texture of a nether portal.
tile.diode.name (#94) Texture of the bottom of a activated redstone repeater.
tile.diode.name (#93) Texture of the bottom of a deactivated redstone repeater.
Locked chest (#95) Locked chest (Texture cant load.)
tile.pumpkinStem.name (#104) Texture of a pumpkin in its growing stages.
tile.brewingStand.name (#117) Texture of the top of a brewing stand.
Cauldron (#118) The top of a cauldron.
tile.null.name (#119) Has the texture of a nether portal but when placed becomes a end portal.
Oak Wood Slab (#125) The texture for 2 oak slabs stacked on eachother.
tile.comparator.name (#150) Bottom of a activated comparator.
This list is not complete and will be updated