For the keyboard, I use a Microsoft Comfort Curve. When I'm not gaming or otherwise wasting time, I'm typing pages of text. Haven't done that in a while though, but nonetheless this keyboard is one that I have grown accustomed to. When using someone else's PC in the house, I get a bad case of typoitis, as the keys are all in the wrong places. I've considered getting a gaming keyboard, but for $20-$30, this one is fairly affordable and if needed, doesn't put holes in my back pocket to replace. And well, I've gone through a few keyboards over the years. As much as having extra and/or programmable keys would be useful, my mouse compensates for what the keyboard lacks.
For the mouse, I use a Razer Naga Hex. With the six side buttons and two additional buttons in conjunction with the typical right, left and scroll button, all programmable at that, the mouse offers utility that a standard mouse doesn't otherwise provide - at least for me. It's comfortable, the sensitivity can be adjusted, and when used alongside Razer Synapse, I can create macros or change what a button does. Currently I have one button mapped to Medi-Gel, which allows me to reload cancel without fumbling over my keyboard using Ops packs, pulling out missile launchers, or using thermal clips. I don't look at my keyboard when playing, well, unless I absolutely must, so it's a big help. Being able to fire off powers and instantly dodge has saved my hide on quite a few occasions, plus the mouse is useful for other games too. I recently learned about Nova-cancelling, super useful in Single Player (haven't played Vanguards in MP yet), but I wouldn't have a clue as to how I'd manage the timing needed if I didn't have the Naga.
As for headsets, I use a Turtle Beach Earforce X12. It's an Xbox 360 model, but works on PC too. The microphone is fairly sensitive, at least when I used it on the 360. As for on the PC, I've yet to have anyone complain about me being loud, I don't talk much though so that could be why (I doubt anyone would want to hear me whine about mooks being cheap). I haven't used speakers in a long time, just the headset for game sounds. Works great in that regard, but I can't stand Banshee screams, let alone locate them accurately from the direction of the scream. Has gotten me sync killed a few times, once on PC and who knows how many times on the 360.
When I did play the 360, first I used a standard wireless controller, then when I bought my own console, the one it came with. Since it was a Halo 4 console, that meant it was a Halo 4 wireless controller. One thing I disliked about the controllers was that using semi-auto weapons was somewhat painful, the controller was comfortable when not using the triggers excessively, but when I did use them a lot, it became uncomfortable fast. I probably should've bought the PC edition to begin with, but I guess changing platforms midway through extended my interest in the game.
TL;DR version: I use a Razer Naga Hex mouse, a Microsoft Comfort Curve keyboard and a Turtle Beach Earforce X12 headset.