Try http://www.parktunes.com/ which lists the songs and links the ones available on Amazon for you to purchase - or alternatively I guess you can also find them in the iTunes store.
Paula's method is one way. For Christmas, DW bought me "Four Parks, One World - Walt Disney World Official Album" which includes these songs and tracks:
You can check out Dis Radio for some great Disney music, including lots of park audio.
However, if you want more park atmosphere music check out Mouse World Radio (just do a google search). For even more access to park music check out Live365 and do a search for Disney music.
"Four Parks One World" CD is good and can be ordered direct from the disney store online.
If you are going to the parks there are several CDs you can choose from. The best selection at DTD that I've found is inside Once Upon A Toy.
I have a 5 CD collection called Walt Disney World Music that I bought in the parks (and I saw it available again inside the parks and at DTD this past Christmas) that includes, Wishes, Spectromagic, Illuminations, Festival of the Lion King, and Parade music. You can find it on ebay also.
About a year ago there was a CD that came out called "Poppin' Guitars: A Tuneful of Sherman" that featured Sherman Brothers music (some park tunes on there incl. IASW and CP). Can be purchased from Amazon for $16.32ea.
Don't want to get in trouble so if you are looking for some other ones so if mods need to delete I will understand.
There is always mousebits.com
That is where I got most of my songs from
I own "A Musical Tour of Disneyland" which was released during the 50th. It was a 6 cd set and major purchase but worth every cent. They also had a double CD of Walt Disney World music released at the same time and it is excellent. I also find websites that list the music of the attraction for example The tower of Terror which I have collected and put on my ipod.
Disney puts some good CDs out. My favorite was when they had kiosks where you could purchase old soundtracks and ride CD's. I made one purchase, "Summer Magic, an old Hailey Mills movie I'm rather fond of but soon afterwords it was gone. A shame really because I also saw a Country bear and a Tiki birds/jungle cruise cd I was going to buy.
I could cry each time I think of all the World Showcase area music someone on the dis had given me years ago. My computer crashed and it was never heard from again (bad pun intended).