Either an LED or LCD monitor, either of the PCS ones are great. I use the G15 gaming keyboard, but there are better ones, this is just nice and modest and a pleasure to type on. Sound card - I use built-in with my surround sound system its still perfect.
Monitor: LG L226WTQ (although I hope to have one of the IIyama 24" LED ones we sell sooner or later)
Keyboard: Logitech G15
Soundcard: Integrated Motherboard Audio.
Personal recommendations here
Moniotor: 2x 22-24" samsung full hd series, dirt cheap monitors that are less than £200 each that also act as full Hd televisions, NEVER had a problem with them
Mouse&keyboard: if your prepared to spend s little more, I prefer razer mice and keyboards
Personal preference here though don't take it for granted that these hardware pieces are better than competitors