Best thing to do is visit electronics stores and use your own eyes as judgement but I'll still give you some general info to help your purchase.
LCD: Cheap in the 30-40in category. Very bright but this usually leads to disappointing black levels. Smaller viewing angle and much slower response time compared to plasma. Thin and light. Good in bright environments.
Plasma: Great black levels and generally better colour and picture than LCDs but lacks brightness compared to LCDs. Response time is practically non-existant which is great for fast action like sports and PES. Good in dim environments. Practically nothing smaller than 42in.
720p vs 1080p: people say you won't notice a difference until you reach 50in+ but really just depends whether your eyes can spot the difference or the distance between you and the TV. If you sit far enough, say 10ft+ for 42in, 720p should look just as good as 1080p unless you have amazing eyes.
Again, your very own eyes will give you the best advice so look at a fair few and choose which one you feel looks the best to you. Also, 'good' hdmi cables have absolutely no effect on visual quality. They just have the name recognition and they're more durable than el cheapo made in China brand but its not really a problem if you don't have pets (or mice) that like to chew on your cables.