Android/Web: Make no mistake, some beer ages well, but others just get gross and skunky the longer they have been on the store shelves. If you want to make sure you're getting fresh brew for your money, Fresh Beer Only for Android (and the accompanying website) can tell you.
The Android app is essentially an extension of the web-based database the site already operates. You start in three large categories: American, Canadian and "International" beers, and then you can drill down alphabetically by brand name.
Once you find your beer, you'll be able to read whether the brewery uses a "best by" date, a bottling date, or some other confusing number to indicate how fresh the beer is and whether the stock should be rotated. In some cases, you'll see a plain date anyone can understand (and the site will tell you how it's formatted and where on the can or bottle to look for it), but in other cases you'll have to decipher whatever code the brewery is using to indicate freshness. Don't worry, Fresh Beer Only explains how you can do it right there in the store.
The Android app is $1.50 over at Google Play, but if you want to try it out before dropping that buck on it, you can visit the site, linked below, and browse for your favourite beers before deciding to take it with you to the store.