I've just succesfully landed my Kerbal Comrades on Duna and returned them, so I figured I'd share a few mods that let that happen.
I declare myself resident rocket scientist.
Firstly once you've succesfully gotten to the Mun unaided, download mechjeb.
This is an autopilot, so now we get to play like NASA and only bust out manual controls for fun times, but if you want to get your payload into planetary transfer and don't want to spend 45 minutes with a protractor and a calculator then this is for you!
Next, part packs.
These are all brilliant for helping build cool shit.
Cool stuff all around, a series of part and section mods that are great for building futuristic looking complex spacecraft.
Kerbal Parts eXpansion
MORE PARTS TO PLAY WITH!
This mod provides a great list of SSTO craft for specific payloads, if you just want to launch station parts and sattelites into LKO but hate re-using crazy and explosive asparagus stages, get this.
FusTek Station Parts
Great for building beautiful space station!
The perfect tool for moving your guys around inside vehicles, no need for pesky EVA transits at 8,000 m/s when they can just walk down a corridor in this mod.