PowerDVD 5 for all my DVD needs. Also I use PowerDVD 5 for a variety of other video formats like DivX, XVID, AVI, VideoCD, SuperVideoCD, etc.
MP3 I still use WinAMP. I don't need a fancy MP3 cataloging program and I never run a fancy visualation graphic effect. Just run WinAMP in the taskbar and occasionally pop it up to modify the playlist. I follow the KISS principal...where I Keep It Simple Stoopid!
I avoid WMP like the plague. It is ugly, slow, irratating when it insists on loading a webpage and the only good feature about it....is that it is free.
I also avoid RealPlayer and Apple QuickTime and hate the way they try to hijack your system. For those times where I have no choice on a website but QuickTime or Real videos.....I use QuickTime Alternative and Real Alternative.