That's right. Think fast!
Figured these contests are cheap, quick, and mildly interesting, so I will try to start one.
Entries can go in this thread, you have a week.
Some guidelines:
1.) Average cost for a cannon: $0
2.) If you would otherwise feel the need to post it in the showcase sections, it probably doesn't belong here.
Some rules:
1.) The cannon needs to work. Video proof or stills/etc. should be included. You have until the end of the competition to prove it.
2.) The cannon needs to hold together for more than one shot.
3.) No cannons that are already posted can be entered.
4.) Only one cannon can be used by the end of the competition per member. Feel free to "practice" or get a preliminary entry.
5.) All forums rules apply.
So, bring on the pop bottles, electrical tape, and Right Guard.
I'll post mine tonight, as the glue is currently drying.
EDIT: Some more info.
I will be cruising this thread and the showcases for the next week. If I'm being slow shoot me an email. Entries will be added to the list below.
Also, feel free to be liberal naming your creations.

Entries
Entry #1 - Clear Chambered Burst Disk Golfball Combustion - mark.f - Verified
Entry #2 - Cardboard Box of Death - jakethebeast - Verified, because tape fixes everything.
Entry #3 - The Coke Can Combustion - Crna Legija - Verified
Entry #4 - SmellRod - Labtecpower - Verified
Entry #5 - Biohazard - Technician1002 - Verified
Entry #6 - Muzzle Breaks - al-xg - Verified
Entry #7 - Balloon Pneumatic - clemsonguy1125 - Verified
Entry #8 - Breech Loading Crush Bottle Pneumatic - whoa044 - Verified
Entry #9 - Pump, Glue, and Tape - qwerty - Verified
Entry #10 - WhipperSnapper - Zeus - Verified
Entry #11 - Home Made Blowgun - wyz2285 - Verified
Entry #12 - Wooden Piston Hybrid - Fnord