As a former band member who mixed and produced our demo, helped with songwriting, and wrote my drum part, what are my rights?

You have rights, your former band members have rights, and the intertwining of those rights need to be untangled. You really need to speak with a lawyer that is well-versed in entertainment law, specifically the music business, because this is a complicated situation and the answer to most of your questions is: it depends.

Good luck.

If you helped write the lyrics and/or music for the songs (not just added a drum beat) then you're a joint author of the "musical composition" in the songs. If you performed as part of the group that recorded the songs then you are also a joint author of the "sound recordings" of the songs (your authorship claim to the sound recordings is also strengthened due to your post-recording production work on the songs).

The songs' musical composition (the words and music) and sound recordings (the masters) are protected by copyright even though those copyrights were not registered with the US Copyright Office. Registration is a good idea but is not required. All joint authors -- such as yourself -- own an undivided interest in the copyrights to their works (the songs). If you're a joint author of the songs then you're entitled to register the copyrights in those songs (even w/o your former bandmates permission) which would provide you with some rights to the song (and a royalty if it ever makes any money).

You need to visit amazon.com, query "music law," buy a few books on the business of music (anything by donald passman is good), and learn about the business side of your art. And then put that learning to practice with your next band -- e.g., have a band partnership agreement, agreements regarding authorship, copyright registration, etc. Also visit http://www.indieguide.com/ and download their indie band survival guide (free).

If you conclude that making a stink about this dispute with your former band won't forever bar you from joining a new band (a real possibility) then track down the "oregon lawyers for the arts" and see if it has a mediation program to help you resolve your dispute. If you belong to a musician's union it may offer mediation services as well. If neither can help, then your local law school may have a business clinic or a friendly intellectual property law professor who may lend you some of his or her time. Of course if you can afford an attorney you should hire one who specializes in intellectual property and is licensed to practice in Oregon (although copyright disputes are governed by federal law, your dispute involves state law partnership and contract issues).

Or you could chalk this set back up as a lesson learned and move on with your life. Write a song about betrayal and angst. And then become more successful than those silly people who didn't want you in their band. Peace.