XRCD's have really really good sound due to the remastering process. Here's a link to a site where they are sold for North America:
The K2 remasters of jazz albums are pretty good sonically as well. And the 24bit Rudy Van Gelder remasters of the Blue Note albums. Concord has bought out the Fantasy jazz label containing Riverside, Prestige and other labels and has remastered a bunch of old jazz and other albums. All that I've heard sound great.
I've listened to SACD on a dedicated system and really liked it but I haven't listened to it outside of that time. DVD-A is another audiophile choice.
DCC, MFSL and Analogue Productions all put out some amazing remasters on 24K Gold. I'm not sure but I think MFSL is the only one of those three left that is still remastering albums. The sonics on all three of these corporations discs are pretty great. If you hunt you can occasionally find a great deal on a 24K disc on eBay but be patient and definitely don't overpay.
There are a lot of good Japanese remasters of rock and jazz out there. One site for them is cdjapan.com. They have pretty reasonable rates depending on the exchange rate of the Yen. However, believe it or not, you can often get the same remasters cheaper from a seller on Amazon.com. There are several who import and sell directly in the US.
In short, there is not one supersite that I know of that has a virtual warehouse of audiophile CD's. Your best bet is to search for remasters of the titles that you are interested in on Amazon.com, eBay, Pricegrabber, half.com,cdjapan.com and that XRCD site. Happy hunting!