Adam's Pure Stock Replicas
It's a very easy craft to fly the best way is to fly to about 70km then burn prograde at apoapsis. If for some reason you fail to achieve a stable orbit it will be fun to watch Sputnik decay in a high atmosphere orbit ;) Action Group 1 to extend the antennas as you will see they will be destroyed in the atmosphere otherwise...
Send Rosetta and Philae to explore asteroids to your hearts content, but be careful some asteroids don't like to be touched.
Voyager 1 & 2
Apollo–Soyuz Test Project
Hubble Space Telescope
Fun and usable orbital telescope launched via the Space Shuttle