Hey, I was playing around with the levitation effect in minecraft 15w31c and came up with the idea to make slime blocks "jump pads".  Now you don't have to have velocity to bounce on slime blocks.  

Those who know how to use the /effect command will know that I am simply checking beneath the player's foot and then giving a levitation effect if there is a slime block.  If you use this specific contraption, then please give me credit.

You can change the hight of the jump by changing the effect command and change what block is the jump block by changing the detect command

/summon MinecartCommandBlock ~ ~1 ~ {Command:kill @e[type=MinecartCommandBlock,r=1],Riding:{id:MinecartCommandBlock,Command:setblock ~ ~-1 ~1 redstone_block,Riding:{id:MinecartCommandBlock,Command:setblock ~ ~ ~1 command_block 0 replace {Command:fill ~ ~-3 ~-1 ~ ~ ~ air},Riding:{id:MinecartCommandBlock,Command:setblock ~3 ~-2 ~ redstone_block,Riding:{id:MinecartCommandBlock,Command:setblock ~3 ~-2 ~-1 command_block 0 replace {Command:fill ~ ~ ~1 ~1 ~ ~1 stone},Riding:{id:MinecartCommandBlock,Command:setblock ~3 ~-2 ~1 command_block 0 replace {Command:fill ~ ~ ~-1 ~1 ~ ~-1 redstone_block},Riding:{id:MinecartCommandBlock,Command:setblock ~4 ~-2 ~-1 command_block 0 replace {Command:"/execute @a ~ ~ ~ detect ~ ~-1 ~ slime 0 /effect @p minecraft:levitation 1 20 true"},Riding:{id:MinecartCommandBlock,Command:gamerule commandBlockOutput false,Riding:{id:MinecartCommandBlock,Riding:{id:FallingSand,Block:activator_rail,Time:1,Riding:{id:FallingSand,Block:redstone_block,Time:1,Riding:{id:FallingSand,Block:stone,Time:1}}}}}}}}}}}}

This was made using MrGarretto's Command Combiner: mrgarretto.com/cmdcombiner