Prior to finding StageTraxx I used to use a program called Karaoki from PCDJ It had a mode for Solo-Singers rather than for Karaoke. The interface made it very easy to play songs on the fly. Had your songs in one frame and the playlist in another. If someone requested a song, scroll in songs frame to find it, then drag it to the playlist. You could then Move To Top to play immediately. I used a trackball mounted on a stand. Downside was I had to drag around a full PC and monitors, and of course the reliability of PC/Windows platform. IPAD is really the way to go.
There are really some good ideas in that program though.
http://www.pcdj.com/karaoke-software/karaoki/