Personally, I gave up trying to find an entertainment center to hold a 36xbr450. I purchased the "matching" TV stand to hold it and I've been using a rack on the side for all my components. Works well for me. TV stand helps to hold my other misc crap that sometimes gets plugged into my TV. ie camcorder, Sega Saturn, etc.
But, to assist your search for an entertainment center, IKEA will be one of the more affordable places to look for to hold that size TV. Every once in a while, Circuit City and Best Buy have some sale on entertainment centers. Places like Scandanavian Designs has a few setups that will accomodate 36" TVs. (I have looked in a while so if Scandanavian Designs and their ilk do not have anything, please don't blame me. :) )
An alternative is do what an ex-boss of mine did. He build his own. For the price of materials and a 6pack of beer, he was willing to build one to my specs. Since he is big into woodworking, it was a pretty good deal. Of course, I changed jobs and states a month after he offered so I didn't take him up on it. One of my other co-workers was though. Something to think about if you know someone with the tools, etc to do it.