Noise Marines
Possibly the most derp thing of all of the grimderp things to come out of Games Workshop, the Noise Marines are Chaos Space Marines sworn to Slaanesh.
What?
Yeah, so Slaanesh is the God of Excessive Pleasure: lots of sex, lots of drugs, lots of weird sex, lots of pain, lots of weird sex that's painful, lots of weird sex while on drugs that are painful. You get the picture. So when it comes to making up a Slaaneshi flavor of Chaos Space Marines, what does GW come up with?
Rock stars, naturally. Rock stars with sound-laser guitars. Because in the 80's, everything was awesome. They've since moved away from giving them actual sonic guitars in favor of sonic guns, but the parallel is still there. Why have they moved away from something freaking awesome into something just kind of meh? Because Games Workshop doesn't know a good thing when it sees one. You really should know this by now.
Even more recently, thanks in part to Dawn of War 2: Retribution and a certain Youtube video they've seen a slight resurgence of popularity. The goofy idea of 80's, Motley Crue-spewing Noise Marines has been replaced with the goofy idea of evil-DJ-esque Noise Marines with long and loud sustained "music" (also known as dubstep) being blasted out of speaker-guns at head-fryingly loud volumes. Also the idea of a Land Raver is pretty cool too.
On the Table Top
The Noise Marines are a strictly balanced choice. Much like any other troops in the Chaos codex, they are very balanced, so will be run off the table by the overpowered Wardian codexes unless supported by other Warp-fueled goofyness That aside, this unit is a less-played but very fun choice.
They come as basic marines, with +1 initiative and Fearless. Naturally, they get the edge on other Marines in close combat, especially a power-sword-equipped Noise Champion (the sergeant equivalent), despite being stereotyped as shooty. That said, you want to keep them as close-range support choices due to their special weapons.
Any model can upgrade to a Sonic Blaster (the new sound-laser guitars, which look like pipe-organ guns). They are profiled as bolters with Assault 2 or Heavy 3 (player's choice each turn), so be prepared to bring down the rain on massed infantry waves. The Blastmaster (which looks like a long-barreled sonic blaster) shoots like an Assault 2 heavy Bolter, or as a small blast krak missile, and both firing modes also have Pinning. Fun on many levels. The Noise Champion can be given an angry pipe organ/mic combo for a backpack, which spits out a S5, Ap3, Assault 1 Flamer, which is fantastic news for you and terrible news for anything near that champion.
The downside, of course, is balance. These guys cost a ball-busting ton. They are 20 points a model, +5 for Sonic Blasters, a Blastmaster costs +40 points, upgrading one to a Champion is +15, his power weapon is +15, the Doom Siren (Angry Organ) is another +15 points, and you'll probably need a transport as well. Thank the dark gods they can hold points.
Tl;dr: The god of rape delivers to those that can afford it.