My friend has a monitor which has his ps3 connected to and his pc, and by the push of a button can switch between the two (Much ike AV1 and AV2 on ya TV)

I want a monitor like this but not a huge one, maybe around 19" or 20" WS

Most monitors with VGA and a DVI or dual DVI input should be able to switch inputs, just look for one with dual inputs such as this

You can also buy stand alone DVI switch boxes which will switch the source, some are rather expensive but some aren't bad.