With wireless data caps and throttling now an unfortunate reality on many American wireless carriers, WiFi hotspots are once again a necessity even for "mobile" devices. If you've got friends and family coming over for the holidays, odds are pretty good that they'd like to borrow your home network for some no-penalty Internet access. To avoid that unfortunate situation where you spend long minutes reciting the amalgamation of letters, numbers and characters you use to secure your WPA2 connection, use WiFi QR Share, which automatically embeds all the relevant information into an easily dispensable QR code.
Because the app requires access to some fairly sensitive password data, you must be a rooted user in order to take full effect. Non-rooted users can only send the SSID of the network. On the plus side, the app has access to all the wireless networks that your smartphone or tablet remembers, which in most cases is also all the networks associated with your Google account. You do not actually need to be connected to any WiFi network in order to share it - the app generates the code without using any Internet connection. Once it's transferred the data, the visitor can simply copy and paste the password when he or she connects.
WiFi QR Share is now in its first release, and so far has near universal acclaim in the Reviews section of the Android Market. If you want to disseminate the code even faster, you can email it directly to others, or just email it to yourself, print it out and let visitors scan the paper. Free Internet: it's a better party favor than fruitcake.
UPDATE: Developer Hostile informs us in the comments section that you can indeed send a WiFi password from an unrooted phone with WiFi QR share, you just have to enter it manually. Also, many QR scanner apps including Barcode Scanner (but not Google Voice) allow you to connect to the relevant WiFi network without any copying or pasting. Thanks, Hostile!