You’ve got 3 (or 4) real choices here for rear projection TVs. I’m speaking from a slightly high-end point of view. If you don’t really care about picture quality and what not, then you can disregard and just get something cheap 
This is longer than I anticipated. There is a lot to cover with these, and I hope I don’t screw up the details. If you have any questions or just want to tell me that I’m posting rubbish, please say so. I’ll post more if you have questions.
CRT rear projection - Best black levels, and if properly calibrated by an ISF tech (at about 400 bucks a pop) it can have the best picture quality (PQ). Worst picture out of the box, and needs yearly calibration. Also can suffer from permanent burn-in, so you need to be careful about watching TV with logos and video games. If you have a wide screen TV but prefer to watch normal cable in 4:3 ratio, then the black bars on the sides can burn in as well. CRT is the cheapest technology right now, as well as the biggest in both size and weight. CRT’s also require you to be almost directly in front of the unit, and eyes level with the screen. Finally, they may not be as bright or vivid as the other technologies.
LCD rear projection - Poor black levels which can be fixed by calibration, but in general look better out of the box than CRT. Some artifacting with high speed shots (like hockey), and other little quibbles that you will only see if you are looking for them. Generally you will get great picture quality with very vivid colours and excellent detail. However, the dreaded “dead/stuck pixel” problem can strike these types of TV. If you get a stuck pixel, the pixel will not change colours as it’s supposed to and will instead stay a certain colour regardless of the signal. Most stuck pixels are not noticeable past a few feet and won’t cause an issue, but red pixels are can be noticeable at normal viewing distance. Stuck pixels are not covered under manufacturers warranty as they are “part of the technology”.
DLP rear projection - Very good PQ, good black levels and excellent details. Almost perfect out of the box, but calibration is recommended anyways. DLPs suffer from the infamous “Rainbow” effect where some (not all!) people can see a rainbow in the screen when looking out of the corner of their eye or when turning their heads. This may not be noticeable in the store as the bright overhead lights diminish the effect. Some people can live with this, and some can’t. Some can’t see it at all… DLP can suffer from stuck mirrors, which can cause either a white or a black square on the screen. Even though stuck mirrors are considered “part of the technology”, people are getting them fixed with no problems. This may change, but for now it’s fairly safe. DLPs also suffer from artifacting, and may be more noticeable than the LCD display.
Both LCD and DLP have user changeable bulbs, where the CRT needs a tech visit for changing the bulb. Bulb life should be about 5 years of 3 hour/day viewing, with some less and some more.
There is a new technology coming in called LCoS (Liquid Crystal on Silicone). This is not readily available and I don’t know much about it.
Brands:
DLP - Samsung makes a good line of DLP RPTV
LCD - Nothing compares to the Sony GWIII line that just came on the market. For an extra 33% you can get the XBR line, but I think that the regular line is just fine.
CRT - I don’t know. I consider the technology dead and haven’t looked into the new lines.
What would I buy? Nothing right now. LCD and DLP technology still need to mature and both have some serious drawbacks. I’m content to wait a little longer and see which one wins the war.