MIDI Explorer Search Engine 
Are you trying to locate a particular MIDI file quickly? This speedy search engine is the place to go. MIDI Explorer indexes nearly 2 million MIDI sound files on over 200,000 pages by file and link name. This dictionary-style search engine will show you all of the different versions of a MIDI and can quickly locate rare songs.

Classical Music Archives 
This site serves up thousands of MIDI sound files by over 1,800 classical composers. Most of the content here is free (but the number of files you can freely listen to per day is limited). A paid subscription (optional) gives you more features.

MIDIsite
A helpful resource that offers over 800,000 free MIDI files. There is also a handy search engine here that lets you quickly find what you need. This site's database is updated daily.

Fresh MIDIs 
Looking for MIDI sound files? At this regularly-updated site, you'll find hundreds of MIDIs, including titles by many popular artists. There's also a forum here where you can post requests for a specific MIDI.