Battery Diag is a nice, free utility from the folks at Rocky Sand Studios and is available on the Mac App Store. The app runs in your menu bar and gives you a quick look at the current status of your power supply and the health of your battery. You can see the current charge level, your battery capacity level, the total number of complete charges and discharges, and an estimate of how long your battery will run on the current charge.
There are plenty of similar apps that have pretty much the same features, but Battery Diag is a nice package that even lets you choose the look and feel of the GUI.
My only complaint is that I'd like to see the battery time remaining up on the menu bar, rather than to have to click on its icon to see that. That information is probably the most important data the app offers, so it would be great to have it persistent. Apple used to offer that info on its Energy Saver menu bar feature, but now, it seems, you can only get a battery percentage in Mavericks. Time remaining on your battery is available with a click on the Energy Saver menu bar icon, but is not visible all the time.
Another similar app with even more info is the free Battery Health app from FIPLAB. It's also available in the Mac app store.