Best Achievements

[Spatzimaus]

For me, it was Jeb's Grand Tour. He went to every planet and moon in a single trip, in a single vessel. For Eve his ship attached to the top of a specially designed ascent stage; for everything else it was an SSTO. (The Kethane mod allowed for on-site refueling, and I have a network of fuel depots.) But honestly, that sort of thing was pretty trivial except for Eve, Laythe, and maybe Tylo. Landing on all the other bodies was just a matter of refueling at the right places. Here's his set of photos from the trip:

The thing is, as you play longer you'll get better and better at both design and execution. On my first few trips I was lucky to make it back alive, but now I can do things like send an SSTO spaceplane from Kerbin to Laythe and back without relying on that whole complex refueling network. (Ion engines for the win.)

[DunaRocketeer]

I guess it'd be what I'm working on now, which is an attempt to make a comprehensive space program. I'm close to getting it all in place, and when I'm done I'll have a modular launcher family, a shuttle, a Kerbin space station, a deep space exploration/resupply craft, a Duna space station and Duna base, a space telescope, a sun escape probe, and a comms constellation around Kerbin and Duna.

[Cmdr. Arn1e]

Greatest thing I've done so far is my WIP Jool-5 mission... 2 planets down, 3 to go! expecting a MASSIVE return on Science from it

[Xavven]

My Eve manned ascent with no Kerbals MIA/KIA on the first try was for sure my biggest accomplishment. I had to leverage the totality of my KSP knowledge to pull it off, including asparagus staging, thrust plates (this was before the ARM patch) rovers, roll cage and rockets to flip the rover back over if it toppled, orbital rendezvous & docking, parachute assisted powered landing, etc. I even had to scout out the landing zone with multiple drones to get a feel for where to put my periapsis to land in generally the right area. Once the lander had a good spot (it lands unmanned), I sent a Kerbal in a rover on a separate launch to go collect science and then drive back to the ascent vehicle. What a feeling when it worked!

[SuperSquirrel51]

First Mun landing, and first Duna landing.

[r4pt0r]

Unlocking the entire tech tree in a single launch.

http://youtu.be/HcWwWAJt4dM

your video made the ksp facebook page. nice m8

[SofusRud]

Building a cargo SSTO that can lift a jumbo into orbit