Some atmospheric effects (clouds and such) for Kerbin and the other planets would be great. Some more planets would be fun too, though I'm willing to wait for those - I haven't even made it to Duna yet! We also need asteroids and comets, with adjustable orbits. Maybe even a "global killer" asteroid we need to deflect Armageddon-style before it hits Kerbin! Customizable colors would be nice; I'd like to be able to paint my ships how I want them to look. And some more uses for bases and space stations are needed, too.