Electro Goo
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This is electricty conducting goo. The idea being pretty obvious - you use it to wire up an electrical source to a device requiring power.

As an added twist, if the flow of electricity ends up going through 'normal' goo, then that goo will burn out, and if the goo touches the ground, then the electricity is earthed. Maybe the skeleton goo could be used as an insulator, for making pylons?

Magnetic Goo
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Lots of fun with this one. You have 2 'poles' of goo (red and blue in this example). As you join together more goo of the same colour, the more it repels goo of the opposite color, and attracts goo of the same color.

So, for an example puzzle, you have 2 threads hanging down. On the end of one thread you build up loads of red structure, and loads of blue structure on the other... but the two are joined together by a single thread. When the thread is broken, the two will spring apart, because of the magnetic repulsion.

The magnetic attraction could be used to 'grab' onto other structures - maybe in a situation where you have to swing a load of goo over to the side of the screen to grab another structure.

Water Goo (Different Use)
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Maybe the water goo could be used to extinguish flames and/or protect the flammable goo?

Sail Goo
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In the windy levels, you can use the wind to your advantage, but maybe goo that was really affected by the wind would allow for some interesting challenges. It might be possible to make structures go underneath obstacles, if the wind was holding everything out horizontally.

Rocket Goo
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I really thought that Chapter 4 was going to see things launched into space. This idea would work well in a space-themed chapter, but is not dependent on it.

In the same way that you can make some goo 'jump' by dragging a direction, you could have rocket goo which fires a rocket blast in the direction you choose. This obviously propels the structure it's attached to in the opposite direction.

The rocket blasts could either be used to navigate a structure through a zero-gravity environment, or be used in a similar way to the way that baloons are used, but with more control.

These ideas are AWESOME! But i think thay are never going to happend.