This TV / monitor combination seems to get good reviews for an all in one solution.
You can connect the PS3/Xbox via HDMI and the PC via DVI and not worry about external sound as it has built in speakers.
Then the bonus of a TV tuner that when connected to an external freeview / Sky box will be digital ready.
20", TV , Monitor and games display seems good value to me at £179.99
Heres the spec
Television Picture Quality
* High Definition Ready.
* 20in (50.8cm) widescreen TV with 50.8cm visible screen size.
* Resolution 1680 x 1050 pixels.
* Brightness 300 cd/m2.
* Contrast ratio 1000:1.
* Viewing angle 160/160 degrees.
* Progressive scan.
* HDMI socket.
* DVI socket.
* SCART socket.
* PC input socket.
* Component video socket.
* Headphone socket.
* 3w RMS power output.
* Auto setup.
* Auto search tuner.
* Auto search sorting.
* Auto search labelling.
* Sleep timer.
* Picture in Picture.
* NTSC compatible.
* Remote control requires 2 x AAA batteries (supplied).
* 230v AC mains operated.
* Complete with tabletop stand.
* Size of TV (H)36.8, (W)49.3, (D)0.7cm.
* Size of TV with stand (H)41.9, (W)49.3, (D)20.9cm.
* Weight of TV 5.3kg
* Weight of TV and stand 5.3k
Currently £199.99 on offer in Argos