The Beer Tracker is a bottle opener with an ingenious second use: a counter that tracks how many bottles it's opened. This is useful knowledge for bragging rights ("Know how many beers we drank last night?") and logistics ("I can only have three beers all night").
The Beer Tracker will set you back $7; it's available from the link above. For a beer opener that might save you money, check out the Spin to See Who Pays opener.