I bought a CoolerMaster QuickFire Storm keyboard with Brown Cherry MX switches for around $80 and it's the best damn keyboard I've ever used... but then my primary use for a keyboard is typing. This one does have a button or two for customizing if you do serious gaming, but not many compared to other gaming keyboards, and it doesn't have backlighting (which I have no need of).

But if you want a nice keyboard I do love these Brown Cherry MX switches, and you can usually get them in a more proper "gaming" keyboard if you want one. They feel a bit like the old Model M buckling springs. (Blues are more clicky than Browns, and Reds/Blacks don't have the tactile bump)

Monitors... Dell U-series seem to pretty popular as a general rule. U2412 and whatnot. It's IPS so it doesn't have the super fast response rate that a lot of TN panels have, but the picture is better and most (not all) find them plenty fast for gaming (I haven't seen any ghosting on my U2211, but I'm not a hardcore gamer).

I use a basic mouse, so I can't comment much there.

Also I think $2k is going to be a good bit more than you need for a good, solid computer. $1200-1500 should give you a solid high-end build. Save the rest for upgrades (or just build a new one in 3 years and sell the current one you're building, or the parts).

Probably want at a 600-850W PSU. Since your budget can handle it I'd suggest a modular one. I hear excellent things about Corsair HX and AX series. I also hear good stuff about Antec, but usually in reference to budget builds. Reviews are your friend (HardOCP has good PSU reviews iirc).

You'll want an SSD. Crucial M4 seems to be the go-to model for that. Samsung 840 Pro I've also heard is good. So far as I know nothing better is coming out soon (but I could be wrong). Samsung Spinpoint F3 was a really good regular hard drive the last time I checked, and you'll want something to pair with your SSD, but I'm not sure if something better has come out since then.

IIRC new Intel Processors (Haswell?) are due out in... March? Maybe? I can't remember. Also not sure on when new Graphics Cards will be coming out.

As I tend to suggest to others, you might also want to make a thread on HardForum.com. They won't like your buying method though, where you intend to purchase piecemeal, but you might still get some useful advice.