If you want one that produces a decent picture, you probably want to be looking at the high resolution ones .... and I don't think you'll get one of those for £40 or less.
I wouldn't bother too much about video either ... especially in that price range.
Nope ... having looked through all the ones on Amazon (you'll probably get better feedback just reading the specs and customer reviews on there), I can't see a hi-res on in that price range.
If I were you, I'd add another £20 odd to the budget and get the bottom end of the hi-res ones.
Failing that, this one:
http://www.amazon.co.uk/HannsG-Hi-Re...886775&sr=8-15
... looks not bad for a non hi-res version.
HannsG make decent budget monitors so the image quality should be pretty decent for a 480x232 screen. Ignore that the tagline says hi-res ..... it's not.
How about £60 for a hi-res one?
http://www.amazon.co.uk/NIX-Touch-Se...887775&sr=8-45
(No reviews though ...)
This one looks like good value too:
http://svp.co.uk/products-solo.php?p...glebase&id=859
9" screen so slightly bigger and 800x480 for £55. Not bad at all.
Or 800x480 with (fiddly by the sound of it) wi-fi for £50:
http://www.play.com/Electronics/Elec...e/Product.html
This one is a bit different. Don't think it's high res .... but you get a weather station! For £40 ...
http://www.play.com/Electronics/Elec...e/Product.html