If you have a Michael's Crafts (or similar MEGA craft store..) Just wander down the sticker and stamp aisles. You will be inspired!!
My favorite was a tiny spider stamp I would use with RED waterproof ink.
Just one little red tick on top of the bottles of a certain batch.
There are also stickers that look like they were made for bottle caps. One of my favorites had 5 different fall leaves. I used each different leaf for 1 of 5 different fall beers.