Large antennas packed into tiny spaces.

[Galane]

http://www.gizmag.com/inflatable-cubesat-antennas/29003/

Make a mylar balloon with the part you want to be the antenna metallized. Add some benzoic acid powder. Expose to vacuum and it inflates. Use more than enough powder and it'll stay inflated for a while with some small punctures.

[nhnifong]

Wow that's a pretty cool design!

[GDJ]

It is pretty cool, but it's been tried before during the mid-20th century with the Project Echo program.

http://en.wikipedia.org/wiki/Project_Echo

[magnemoe]

It is pretty cool, but it's been tried before during the mid-20th century with the Project Echo program.

http://en.wikipedia.org/wiki/Project_Echo

Not entirely, the cubesat uses benzoic acid powder who might be the same as Echo used however only part of it in metal and it has an antenna inside making it an inflatable parabola dish.