I've used beer in my injections before, generally mixed with apple cider vinegar. A couple of times I've made a lime injection and used Bud Light Lime mixed with lime juice. This turned out decent, but was better in chicken than pork butt, though.
Generally I've found that cheaper domestic beers work best, otherwise you're walking a fine line with having an overpowering beer/hops taste which some people aren't big fans of (ie. my wife).
Other things that work well as injections and sprays are whiskeys and rums, straight or mixed with apple juice, apple cider vinegar, or heated with brown sugar to make a delicious syrupy glaze. Just ideas!
