Audie--this is long. I've been cooped up at school all day.
If you don't have an older brother, you should get one:
LP: I don't remember ever purchasing an LP, but I have a nice-sized collection which includes the Disney stuff. I think those were technically the joint property of me and my brother, but he didn't listen to them much. I can still quote many of the story albums verbatim, and am liable at any given moment to burst out singing something from "Pete's Dragon" or "Bambi." (Sing along if you know it: "Dragon liver can cure a cold! Dragon powder grows hair--gasp!--With dragon blood you'll never grow old...!" or "Let's sing a gay little spring song--whoo! tra-la-la! This is the season to si-ing!")
The first one that was ever exclusively mine was The Carpenters: The Singles 1969-1973. It was a present for my 4th Christmas because "Top of the World" was my favorite song. Still love that album.
I later stole my brother's copy of "Destroyer" (Kiss) because I loved the song "Beth." (Peter Criss told us the pitfalls of marrying into a band long before Steve Perry ever sang "Lovin' a music man ain't all it was s'posed to be...") When he was in college I requisitioned his entire collection on the grounds that I had a record player and he didn't.
45: The first 45 that I had was "Summer Nights." My teenaged cousins were singing it, so I had to have it. Juice Newton's "Angel of the Morning" got a lot of use, too. However, I stole "Rubber Buscuit" from my brother and it was probably my favorite.
8-track: I personally owned Air Supply's Greatest Hits. I stole the Village People "Cruisin'" and Queen's Greatest Hits from my brother. I still play both of them when I'm doing home improvement type stuff. I requisitioned the rest of his collection, including some Jimmy Buffet, on the grounds that he wasn't around to stop me.
Cassette: My parents gave me "Hooked on Classics" when they gave me my JCPenny stereo. I don't know where it is now, nor do I know the first cassette I actually bought. As you may guess, I have an impressive collection that was stolen from my brother, (on the grounds that he didn't know I stole them all, and, besides, I gave him a bunch of them for birthdays and stuff) including all of the works of Eddie Van Halen. I won't name the rest because you'll just drool.
First CD? No idea. Maybe Journey's Greatest Hits. Why would I need a CD when I can hear the Village People sing "Hot Cop" on 8-track?
Stones too. 