Based on historical popularity and preservation interest, these are frequently downloaded titles found within archive.org sets: Xbox 360 Store and Xbox 360 Marketplace FAQ | Xbox Support
However, the cat-and-mouse game continues. Savvy uploaders use workarounds: archiveorg xbox 360 roms top
Files for microsoft_xbox360_digital_part7 Files marked with are not available for download. Internet Archive XBOX_360_XBLA directory listing - Internet Archive archiveorg xbox 360 roms top