PlatypusBudget: 2000-2500
If you're not going to wait for Haswell CPUs release. I've picked CPU cooler because even at stock speeds it can reach pretty high temperatures. I would still suggest that you should overclock, it's not hard and you'll be able to get more FPS, you'd just need to change the i5-3570 to i5-3570K.
PCPartPicker part list / Price breakdown by merchant / Benchmarks
CPU: Intel Core i5-3570 3.4GHz Quad-Core Processor ($204.17 @ Amazon)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($24.99 @ Newegg)
Motherboard: Gigabyte GA-Z77X-UD3H ATX LGA1155 Motherboard ($139.99 @ Newegg)
Memory: G.Skill Sniper Series 8GB (2 x 4GB) DDR3-1866 Memory ($69.63 @ NCIX US)
Storage: Crucial M4 256GB 2.5" Solid State Disk ($199.99 @ Newegg)
Storage: Western Digital Caviar Black 1TB 3.5" 7200RPM Internal Hard Drive ($88.98 @ Outlet PC)
Video Card: EVGA GeForce GTX 680 4GB Video Card ($539.99 @ NCIX US)
Case: NZXT Phantom 410 (Black) ATX Mid Tower Case ($84.55 @ Amazon)
Power Supply: SeaSonic 620W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply ($76.50 @ Newegg)
Optical Drive: Asus DRW-24B1ST/BLK/B/AS DVD/CD Writer ($19.96 @ Outlet PC)
Monitor: Asus VG248QE 144Hz 24.0" Monitor ($266.99 @ Amazon)
Total: $1715.74
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-05-10 12:10 EDT-0400)
As for the peripherals, I don't know anything about keyboards, you might want to take a look at the forums here, I've seen some posts/threads about mechanical keyboards.
For the mouse, I haven't really seen mice with 3 buttons for quite some time right now, most of them are made with 5 buttons. I was used to 3 button mice, but when I had to make a switch to 5 button one the extra 2 buttons didn't hinder me and I actually find some use for them.
These are my favourites from seeing reviews/using them. All of these have nice sensor in them.
Zowie FK
Zowie AM
Zowie EC1/EC2
Razer DeathAdder 2013
Razer DeathAdder
Razer Abyssus
Logitech G400 (I've heard it's discontinued)
The DeathAdders build quality isn't that good, but mine has been going pretty strong for ~2 years already.
Mouse pads, from what I've gathered these are the ones that are mostly used:
Razer Goliathus (I'm using this one myself, it's pretty nice and it's quite sturdy, I've washed it a few times and it always comes out clean, just like when I bought it.
PureTrak Talent
Steelseries QCK