I too use JRiver Media Center and love it! It's a slick really program, one of those things where you just know they got it right.
Can't say that I've noticed any differences yet between Versions 17 and 18. I know they've made a lot of tweaks, but I mostly just use the basic stuff.
For those not familiar with it, here is their website:
http://www.jriver.com/index.html
I have to wholeheartedly agree with punks15 on his statement, "and the theater view is awsummmm".