Check out my latest find, a super cheap (£20 brand new) Logic3 PSone LCD screen. I figured that is was gonna be a load of cheap crap but to my surprise it's actually very good. The picture quality is fantastic, my only gripe is the sound's a bit tinny but hey, you can't have everything. And of course, it is very easily TATE'able!
Right, I'm off to play Strikers 1945 II and Gradius Gaiden in the car!!
I have one of the old 4" screens by InterAct, which I paid $180 CAD for when it first released, and I've gotten countless hours of service from it. Unfortunately my PSOne has been lent to my sister for the last 3 or 4 years, but I bought a new power supply for it and I continued to use the screen until a few weeks ago.
At that £20 price though, it's almost worth it just to buy a couple of extra ones just to hack out the LCD screen for portablising consoles.