The main channels available for publishing Apps are the following:
- Marketplace (Not available right now, see http://blog.mobincube.com/nice-try-microsoft/#more-623 )
- Play Store
- App Store
- Keep in mind that there are dozens of other markets out there which can help you reach more people.
You can also make your Apps available through QR snap images and ordinary URL links for download. Remember that the advertisements can be done outside the digital world, for example with a poster in a cafe or on a business card.