LED is a just a form of LCD. What it does is allows the LCD to have better blacks, contrast, and colors. While not up to Plasma standards, its far beyond what normal LCD can do. But you pay a huge price premium for this feature. You can get a better plasma for less. Also, it doesn't solve the inherent motion blur problems of large sized LCDs.
LCD vs Plasma
LCD - is the everyman HDTV. It is cost effective, hence its popularity. It is also physically lighter than Plasma. It tends to draw less power than Plasmas as well (though good Plasmas are now competing with LCDs). It has a matte finish so is useful for rooms that have too much ambient light which can not be controlled. LCD whites are a bit brighter than Plasma whites (but how often do you crank your brightness to 100%). LCDs are considered better for gaming (but I don't think you'd be disappointed with gaming on a modern Plasma). LCDs are sharper in SD (think evening news instead of film); this isn't a good vs bad, its just a personal preference thing. LCDs also have a bit more muted colors; again this isn't good vs bad, its purely personal preference.
LCD technology has problems with fast motion though. That is why you see ones advertised with 120Hz or 240Hz refresh rates (100Hz and 200Hz in Europe). This does not come close to Plasma though. So they aren't as good for fast motion (sports and movies). The 240Hz ones are making good strides, but right now you're paying a HUGE premium for it.
LCDs are also not as strong with their ability to reproduce true blacks. Their blacks tend to be a bit grey and not a true black. LCDs with LED backlighting are coming out now though. These are finally starting to bring LCDs to the Plasma level in terms of blacks. However, like the 240Hz refresh rate, you must pay a large premium for this feature at the current time.
Plasma - they have better blacks (true black), contrast (greater ranges in blacks/whites so you get greys instead of clumps of black and white), and motion playback (their refresh rate is near instantaneous much like old CRTs were). Their overall image quality is better than that of an LCD. While prices on them are constantly dropping, they do demand a slight premium over LCDs of a similar category. The colors in Plasmas tend to have more "pop" to them; this isn't a good vs bad thing, its just personal preference. Also for SD viewing they are a bit "softer" (think more like film less like the evening news). This isn't a good vs bad thing, its personal preference. Most plasma owners get used to it and don't mind it.
Plasma's are glass though so are glossy. They can have reflection issues if you are in a room with lots of light that you can't control (you can't turn off the lights and you don't own any blinds). And good Plasma care would require you condition them. But its fairly simple to do. All you have to do is keep the brightness and contrast (picture) settings cranked way down for the first 100-200 hours, then optimize, and you'll have an amazing TV experience.
Plasma myth (1) - They experience burn-in. This is inaccurate, those days are gone. Just condition the gasses and then use it as normal and you're fine. Also, the better sets have built-in features to prevent this (on top of the technology just generally being better now than say 5 years ago).
Plasma myth (2) - They have short life spans. This is another inaccuracy. Most are now rated in the 60,000-100,000 hours range. At 8 hours a day 365 days a year that would mean a life of 20-30 years. So do you think you'll still want/own the same TV in 15 years, let alone 30?
Plasma myth (3) - They won't work in high altitude because of problems for the gasses. This is again no longer an issue. Current Plasmas can be purchased and used in mile high Denver, and above, so you'll be fine where ever you are (unless you're living in the Himalayas).
Plasma vs LCD - One important note though is TV size. In 42" and above you see and get the benefit of the Plasma advantages. But 40" and smaller and the benefits are diminishing. So if your needs are for a smaller television, LCD may be a wiser choice.
Plasma brands - Pioneer Kuro Elite is the best, followed by Pioneer Kuro. But these can cost as much as a small car. Panasonic Viera is the next best and is much more cost effective. The Vieras can give the Kuros a run for their money (they might not win, but they are no push over in quality). After that I would look to Samsung primarily as a Plasma option. There are also some LG models that have reviewed extremely well (but do your homework).
LCD brands - I would stick with Samsung, Sharp Aquos, and Sony (but only Sony if its on sale, otherwise it tends to be overpriced). Sony stopped manufacturing LCD panels, they now buy/use the same ones used in the Sharp Aquos sets. Samsung is a step above the rest if you go with the series 6 through 9 models. The series 4/5 are strong performers as well, but a bit better