New added uses:
Part 1 (What we can do without adding blocks)
1. Make Soulsand
This isn't the most useful of all the suggestions, but it makes sense to be able to make soulsand out of slimeballs, zombieflesh and sand, in the following pattern:

(Zombie Flesh Idea courtesy of Gurkudrengur)
(Lower amounts of soulsand idea courtesy of The_Creepers_Friend)
(Image and final recipe courtesy of Jassycats)
2. Throwing option
Slimeballs should also be throwable, much like snowballs. Like snowballs, they wouldn't do much except for push back mobs/players. However, throwing one at a Magma Cube or Slime will heal them, while throwing them at boss mobs will damage them (at the minimal damage an arrow does). This would allow an easily spammable, but not over-powered weapon for people to use against the Enderdragon/Wither. However, like arrows, slimeballs would not work against the Wither once it gets beneath half health.
NOTE:
a. Many people think that there should be a temporary slowing effect when thrown. What do you think? Comment below, please!
b. Should slimeballs be able to do damage through brewing or other means? Please comment below on this, if you have an opinion.
3. Potions of Slowness
There are several potions that players are currently not able to legitly obtain, one of them being Mining Fatigue. I think that slimeballs would be a suitable ingredient for brewing a potion of Mining Fatigue, as they give out a feeling of "slowness" to me.
4. Spawner Takedown
Right now (especially on adventure maps), spawners are a big challenge for players to take down. Why not be able to use slimeballs to slowdown the rate of spawning? If say, the amount of time between each spawning is 6 seconds, then the slimeball would reduce the spawn time to 12 seconds (note that the numbers are made up). However, this would only apply for 3-5 spawn cycles (not sure how many it should be exactly).
5. (NEW!) Anti-bonemeal
What if there was a way to stunt growth for plant growth? This would give potential for griefers to cause havoc among farms, but the upside to this would be that one would have a chance of a double harvest in the end (as in 2 wheat, 2 pumpkins etc...). This would allow people who don't have the time to visit their crops as often to get more out of their time, as they could spend the longer growth time doing other activities, and then come back and obtain more resources than they would have.
Part 2, (New blocks and stuff)
1. Rubber!
-WIP- and open to suggestions!
This great idea came from ZonbiTara, and would involve smelting slimeballs to obtain a rubber item. Uses would include making a trampoline (basically a block that, when one jumps on them, lets one jump two blocks high). This would be a simple way to allow one to reach otherwise inaccessible places.
A slimed version (or default, I've not decided), would only give the higher jump when there is a redstone current.
2. Sticky blocks
-WIP- and open to suggestions!
A novel concept combining ideas by Fireheart0011 and tonytwo, sticky blocks would allow blocks to gain some sticky characteristics. For example, craft a slimeball and sand to get 1 block of sticky sand (which wouldn't be affected by gravity). The same would go with gravel.
EFFECTS:
Sand/Gravel: Sticky sand/gravel is not affected by gravity, with only slight difference in look! However, when a redstone current is run to the sticky sand/gravel, it becomes a normal block, giving it use in traps and other mechanisms.
Noteblock: Adds a muffling sound effect over all notes played, giving notes a new sound.
Fireworks: Adds a new effect (particles remain seen for longer)
Bedrock: Lessens void fog in the surrounding 5x5 area, centered on the slimed block.
Any suggestions for more blocks to be slimed? Add in your ideas!
3. Slimeblock and Glue
-WIP- and open to suggestions!
The slimeblock would be crafted from 9 slimeballs, and would freeze any player who enters it for several seconds, and it would also apply the "Nausea" effect. This would be a decent trap and deterrence against griefers.
When shift-clicked onto a block, the slimeblock works like conventional glue, and would allow the next placed block touching that surface to stick to the block. To remove the glue, one would simply mine one of the blocks, breaking the glueing effect. The practical applications of this would include saving on pistons, more compact redstone designs, movable structures (such as statues or even houses) etc.
Currently 26 Supporters!
1. Krontical
2. JTTCOTE2
3. peterdetmig
4. ZonbiTara
5. Goldformeh
6. Firehear0011
7. Gurkudrengur
8. the EPiK1
9. Brinjal66
10. rorybg
11. Calvin1119
12. KingTrygon
13. Deonyi
14. Pencilshavings5
15. nacho1309
16. endercreeper444
17. sugarmaster1
18. Swam_Ruan
19. CreeperSpy88
20. eddy7223
21. The_Creepers_Friend
22. CreepsInMyMind
23. SupaDipanBaby
24. spiderraptor42
25. Jassycats
and me, Werds
1
Some of these up sides include defining if a bed belongs to a certain player. It would be useful to define a players bed so they don't continually sleep in another players bed. This is a sort of realism that doesn't necessarily interfere with the flow, or gameplay of Minecraft.Another up side would be it would allow you to express yourself to other players. I do realize you CAN express you originality through other things such as your creations, skins, etc. It would just be another way to make your multiplayer or even your single player home look better than ever. Creating your sheets is as simple as dying leather armor. All you have to do is gather your specified color (or dye) and find the nearest crafting table. Next you would need to line the perimeter of the slots with wool and then fill the middle with the dye that you have collected.