Ferram Aerospace Research
So far, this list has focused on mods that add things, improve things, or make things that little bit easier. Masochists: I've been neglecting you. I'll make it up with FAR, which completely reworks KSP's aerodynamics to better simulate rocket drag and aeroplane lift. What that means in real terms is that will crash more. A lot more.
A new Flight System widget keeps track of just how much trouble you are in. Climb too sharply in your spaceplane, for instance, and it will inform you when minor stalls occur - something that becomes more visually apparent when you experience a major stall. To help you get to grips with these new laws of physics, a selection of pre-built vehicles can be loaded to give you an idea of their best building practices.
Install if: you found rocket science too easy.
KSP's EVA (extra-vehicular activity) options are great. Pop a Kerbal out of his ship and you can make data readings, plant flags, and… er, jump about a bit? Okay, currently they're pretty limited. That's something the Kerbal Attachment System mod is designed to fix, and it does so through an ingenious array of tools that your Kerbals can interact with once they've landed their vessel.
The parts KAS adds are designed to be securely fixed to the ground. Through them, your Kerbals can bolt together winches, struts and pipes to build elevators, cranes and anchorings. This lets you create off-world pit-stops, performing resource transfers, permanent base construction and vehicle towing. All of the new parts will fit inside of containers, which can be attached to your ship for easy interplanetary travel.
Install if: you like to go hands on.
The misspelling of laser never stops being annoying, but Lazor System offers more than enough features to make up for it. Installing one of its laser modules enables a variety of effects, from the mundane but useful, to the spectacular but impossible. The docking camera, for instance, gives you a greater view of a tricky orbital procedure. The tractor beams, on the other hand, are less routed in sensible science.
It gets stranger still. A teleportation system lets you beam Kerbals down to a planet's surface, while the remote resource transfer can warp fuel across a 10 km gap. An included achievement system will also track your greatest moments, be they through hard work or sci-fi futurism. For the less pacifistic among you. Bombs, missiles and weaponised lasers can unleash destruction on the once peaceful worlds.
Install if: you really like Star Trek.
Kerbal Multi Player
KMP has been out for less than a month, and its creators stress that the current build is a highly experimental alpha. Still, it's a multiplayer mod for KSP, so I couldn't not include it. Things will go wrong and it will regularly refuse to load, but on the occasions that it does work, the experience of loading into a universe that's teeming with life makes the whole thing worthwhile.
Because there's no server browser, you'll have to load manually enter your intended destination. A quick internet search will bring up a few dedicated communities that are already exploring in tandem. Alternatively, a separate download gives you the option to start your own server. Once you're together with a group of people, head to the Tracking Station to see what they've been up to.
Install if: you want a multinational space program.