Corsair for headphones, Razer for mouse, and keyboards are pretty flexible. However, Corsair keyboards ARE pretty good. As for pre-built computers, I’ve heard good things about Corsair.
Corsair VOID (as Toast said) is very effective, headphones I use.
Razer’s Naga Trinity mouse is a complete beast. The 12 button setup allows for a lot of different plays to be made efficiently.
And lastly, keyboards- any old one will do, however I’d suggest one with a wrist pad. Mechanical keyboards are also good, in my experience the keys aren’t as prone to falling off.