I don't think that there are any TVs on the market yet with 4 HDMIs, but some now have 3. In the meantime you're probably best to get a splitter. The mag has looked at some already. Think the QED one did well as it's powered and doesn't damage the signal too much.
Kiddo, what four machines do you have with HDMI outputs? Some of the bigger AV receivers have four HDMI in/one HDMI out, which might work for you...
I was in the local audio/visual shop at the weekend and i think it was the panasonic that had 4 hdmi sockets, you caould always drop the dvd player with the new firmware update for the ps3, i find its better than my upscaler
You can just prioritise and downgrade some components to component.
Otherwise probably more likely to find a 4 way switch, or more commonly a 3-way switch and a TV with 2 HDMI inputs. (JS Technology to an excellent 3:1 HDMI switch for £145).