[updated and corrected this topic from earlier today]
This weekend I finally got around to uploading dozens of NEW music files recorded right here at Digital Press HQ, directly from MAME. The tracks include a slew of video game theme music and sound effects. I haven't added descriptions yet but I did put the new ones right up top, they're easy to grab and play.
http://digitalpress.5u.com/dpsoundz/
Nothing new in the SID page, but Sound Effects, Music, and MP3's... you'll see 'em as soon as you open the page.
Have fun!