Pound for pound plasma is much better at colour and blacks, along with smooth motion.
The best Plasma's are by Pioneer, but very very price for there Kuros (hope i spelt that right) but a very close second is Panasonic Viera, i have one the 81 range. Mind blowingly good for the price.
Top spec LCD's are pretty these days and better match up to the Plasma's, but the old age thing of image retention on plasma's is pretty much out of the window on the new higher spec models, i play the WII and xbox 360 on my plasma without any issue at all, although my old LG plasma did suffer i wee bit, but nothing the inbuilt white wash wouldnt solve, but something to bear in mind if having static images for long peroids of time.
In terms of LCD's Sony tend to be the ones to go for, closely followed Samsong, ok the blacks will not be as black, and they do tend to suffer slight motion bleed, and will not match the SD image IQ that plasma's will produce, there HD IQ isnt a million miles of plasma, and SD IQ will be more then adequate for most peoples need's.
The larger the screen gets the more notice the difference between LCDs and plasma generally due to the costs most manufactors do not build plasma's below 42inch, and LCD's become more expensive to produce at larger sizes to get IQ's levels to be a match for plasma's.
Provided you are not going to be displaying pics more then 5minutes static you should be fine getting a plasma to which id say the Panasonic being the best compromise for money and image IQ, the 81 series having inbuilt Freesat is handy, as you can recieve free HD channels on it, and simply stunning SD image IQ, and mind blowing HD. If you are going to be having lots of slide shows of static images for longer periods of time then LCD would be the wiser choice, as screen burn hasnt been completely resolved on plasma's, although dont be fooled by some, screen burn can happen on lcds but there much better at handling static iamges. In which case the Sony W4000 is pretty tasty.
Providing ofcourse you have around £1,000 to spare.
Oh and yes SKy only broadcast in a max of 1080i, but the difference between that and SD is mind blowing, but id prefer to get a 1080p tv set, as i think that will become the norm, as wil 24fps, the Panasonic 81 will do both, pretty sure the Sony W4000 will too.
One other thing to bear in mind too, plasma run hotter, some like the Panny i have has has to control the temp, but i cannot hear them, they keep the set very cool. some cheaper plasmas dont have any so can buzz slgihtly if they get very hot, and you will find them dishing out alot heat.
LCD's do not have this heat issue with them.