MN,
With a 13'x18' home theater room and a $10K to $20K budget, you are definitely going to want to consider your options. Plasma is great, and I think that it has a bright future (pun not intended), but you could really do something pretty special with a front projection system in your room.
You can't beat the immersive theatrical feel of a front projection/screen system.
Early warning: You are probably going to get an earful on this topic, as it is just about a daily conversation piece at this place. The folks are friendly and helpful, and will probably guide you to the 2-3 best projectors for your situation...but they will each have their pros and cons.
You will then need to decide what is most important to you and get the demos of the "short list" to make a decision.
Tell us as much as you can about the room, and maybe we can offer some ideas.
Questions
* Do you have complete light control?
* What is the composition of the ceiling? Do you have exposed beams?
* What is behind the rear wall? If your room allows it, you might be able to install a projector in a "projector closet" like a movie theater. See
theaterphile.com for pictures of my home theater for ideas.
* What types of source material would you be using? Do you get HDTV in your area?
* How big can you go with your screen? Related: how large are your front main speakers, and would they interfere with your screen width? With a room that is 13' wide, your front mains may be the limiting factor on screen width if you plan on having the speakers flank the screen.
* How computer-savvy are you? A strange new discovery is that a correctly-built computer can compete with high-end scalers for great picture quality, but at the expense of ease-of-use. This is another common question to struggle with.
Anyway, tell us whatever you can, and you will hear a lot of opinions on the topic. Keep in mind that most folks who have gone through this process believe that they know what the best choice is (after all the research), and will be somewhat biased to recommend their own equipment (myself included). That is something to consider as you are making some decisions.