don't kill yourself over making it HD compatible... i've got a 20" LG and there's borderline ZERO difference between that screen running HD (via HDMI to DVI) and that screen running via Svid.... you need to be <4ft away to see any difference and that's only really for text....
That was £202 from Scan.co.uk and is a pretty decent all-round screen.
Also... before that I had a £152 20" LCD from computersupermarket.com (NQ211).... as reviewed in Sept07 "What Hi Fi?" NB: that's LAST month's magazine!
For the money it's a great screen.... BUT it is limited in functionality: sound is awful (need external speakers - otherwise it's a laptop speaker in the tin-can!), it is noticably less black than the LG and most importantly... the connectivity is not up to much: DVI is NOT HDCP compatible (the LG is!!) and there's no component (Pr-Pb-Y / YUV) line in (which the LG has) and no SCART, so there's no convential HD option and no straight-forward RGB connection over SCART (you'd have to do VGA to RGb and then RGB to SCART)... and the TV tuner (analogue) is shocking...
That said - it does have a very decent viewing angle (vertical and horizontal) and has a great picture via HDMI/VGA (RGB D-sub)... and it's very good with Svideo sources and composite.... well, it is composite...
If it's strengths fit your requirements, then it's a great screen... as a proper media solution, the LG is leagues ahead (speakers, SCART, composite and HDCP DVI).... but costs 30% more.... marry it up to a £15 pair of 2.1 speakers (as I had) and £60-odd digital tuner that outputs to VGA (Gadmei 6808) and you'll have a really decent little bit of kit.
There is a 19" version of the LG for £174+delivery.... which might do the job very nicely for you.... just not sure it it's quite as well equipped.
edit: you say "HD"... but what is your source? DVI / HDMI / component?
wrt to contrast ratios and black levels.... it's all relative and it's all dependant on quite how honest the manufacturers are being... the argos screen you quoted says 450:1.... the NQ211 is 1200:1... and the LG is 3000:1... I'm not sure if the NQ211 or the LG are anywhere near what they claim, but the LG is significantly better then my old Sharp Aquos!
But that said. the NQ211 is probably better than the LG if you're not quite lined up properly... but dead-on, the LG has it utterly caned.