There are a number of good receivers out there and depending on the price range you are looking at will determin what brand is best to buy from. One price range might be better with one brand while a differnet price point might be better with a different brand. It is wierd but for example there are differences even in the same price point with scalers used and connections and internal amplifiers.
Sony - I have some Sony gear that I am happy with but I honestly wouldn't touch there receivers with a 10" pole. IMHO I do not like the overall sound and feel the amplifier section is on the anemic side. And I can not say I am a fan of Sony's room correction ether! I am sure that there are a number of people here that will not agree but this is my honest opinion. Yes they have alot of inputs which is nice and if Sony made a great receiver I would consider it for the prime spot in my home theater. But right now you will not see a Sony receiver in my home theater!
Denon - I personally love this company and have been impressed with them for the past 8 years. Denon IMHO does a great job at intergrating the technology, they have great specs, very good sound, Audyssey, lossless decoding and are built very well.
Onkyo - I do not care for there lower line especially with the component video on many of there receiver models being cut at 50MHz. But you can get alot of HDMI inputs, lossless decoding and features with Onkyo for the money.
Harmon Kardon - Depending on your needs a Harman Kardon might work well but IMHO HK has fallen behind the likes of Marantz, Denon, Yamaha and Pioneer Elite.
You might want to take a look at Rotel, they have some new models with lossless decoding, good amplifier sections and HDMI connections. Adcom is a great sounding receiver but I am not sure you will find one with lossless decoding. If you have a Bluray that you do all the decoding and do not care if the reciever can decode the new lossless, then you should give Adcom a listen they are a great sounding receiver and there amp sections are well above the Denons, Yamaha's, Marantz's and Pioneers.
As far as Marantz goes, I have never heard anything about the Audyssey being disabled and especially I have not seen anything about it on any reviews. But I do know that the Marantz line has very good sound and they do offer all the newest format decoding and conductivity as well.
Also give Integra a listen they are a great sounding brand as well and they have all the toys like the Onkyo lineup. Then there is also Sunfire and Anthem as well for receivers to consider. I would just match your needs and listen to as many of the models that meet your budget and requirements.
Denon and Marantz are owned by the same company, and then you have the another company that own Onkyo, Integra and Integra Research. I would listen to and check out as many brands as possible so you can be confident that you got the best receiver for your needs and budget.

Personally I am looking at the following brands, (Denon, Onkyo, Rotel, Marantz and Adcom) So far I am leaning towards and saving up for a Denon AVR-3808ci.
Edited by Dave Moritz - 8/28/09 at 3:13pm