well, there is an old soundjam beta floating around for OS X. By the way, iTunes was based on and had many of the same programmers from Soundjam. Anyway, Audion seems to be a popular pick among the anti-itunes crowd. The only problem with that is that its not free, but it does have some cool features and is totally skinnable.
itunes is pretty nice, although its a ram/cpu hog for sure.
If you wanna be brave, pick up mpg123 from: http://macosx.forked.net/
its a command-line mp3 player (great for scripts and pranks - like sshing to your friends computer and playing the Phantom of the Opera).
I wasn't too keen on iTunes, so I bought Audion at one point. Now I use iTunes exclusively, it does everything I need, except one thing for which I keep Audion around: Audion has an MP3 editor. I recorded one whole side of a tape on my Cube, converted it to MP3, opened it up in Audion and had a very easy time of cutting it up into separate songs (copy and paste into other editor windows). I like the way iTunes handles playlists more, but thats because the only advantage Audion could have in that area is in its linked playlists (a playlist is just a folder on your HD, moving songs there is actually moving them in the finder), but in my experience, if you have a huge collection of music (like me: 5000+songs, over 21 Gigs) it's just insanely slow. Anyway, that's my two bits; anyone else is welcome to share other experience...BTW, I may have a copy of the soundjam beta for X somewhere, if I dig it up tonight I'll post back here about it.
If you aren't a fan of iTunes I'd definitely recommend using Audion, it's a great looking player and has the MP3 editor (like sheepguy42 said) that iTunes lacks...download it for free and try it out, you may find that it is worth your money
Back in my OS 9 days I used Macast for the longest time...I actually wonder now what happened to this program. You don't really hear about it anymore, even though back in the day it was perhaps the best mac mp3 player available...