LED is a type of LCD. It vastly improves blacks, colors, and contrast for LCD. But it still suffers from motion blur problems. So you need one that is 120Hz or 240Hz refresh rate. The combination of LED and the refresh rate will cost you a LOT.
DLP is a great price option for large sets, but its a dying technology. Only Mitsubishi is still developing sets. Everyone else has walked away. Also, while the overall set is super reliable, you have to constantly replace the bulbs. The bulbs have a life of 1-4 years (depending on bulb and how much TV you watch). You can change them yourself, its easy. But its not cheap. A new bulb is $200-$250 at least. Its got great image quality though (just below plasma) if you're willing to deal with the long term bulb purchases.
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.