I know that indexed PNG (further coptimized with the PNGOptimizer or PNGout) results in very small files.
Its the standard format for Mobile games.

From my tests, the PNGs worked good as Panel elements.

http://www.opserver.de/ubb7/ubbthreads.php?ubb=showflat&Number=350355#Post35035
revenge of the titans which is part of the humble indie bundle #2 in my opinion has a very nice graphical style that would be well suited for saving space.

i also have some ideas for small games but i am not sure yet if i will have enough time. probably i will be busy with too many other things at the beginning of next year.

I am already at 140 kb zipped (exe only)...

Any idea where I can get free midi ambient music?

My project currently is 25 kb zipped (without DDLs, only whole script with small demo level and models).
I'll not spend time on design and so on, I'll just use exactly the same design as game VVVVVV.
Exactly like this:

And the main idea will be same, it will be sidescroller with gravity changing...
I hope it will be enjoyable for all of you.

I´m in, for relaxation and challenge.
63kb unzipped, only code, no ressources.
Mainly mesh generation, sound generation and bmap processing
(drawing, blurring, blending, noises, brightness, contrast, magic wand function...)

I don´t use arrays to dump or define bmap´s or meshes.
Everything is generated through math and a lot of loops or recursion.

But I won´t show any images, yet.

I would've joined if I had the time. Sorry, but I'm off to the equator over break.

I like the small-contest-idea though and will be watching out for all your entries!

Fleeing the cold?

I'm snowed in. ^^

@3run :
I really like the simple and clear graphics of your retro game !

Its is some Little Big Planet Retro version ?

I hope you'll put some good gameplay elements(hook, or mounted reactor to fly , etc ...)

Thank you for your kind words But that picture is not from my game, it's from VVVVVV platformer. But my game looks same too. Search for VVVVVV in youtube. If you want to see some gameplay elements just PM me with your ideas