Can we get "Enqueue" or something similar in iTunes [10.7]
The current (and previous) version of iTunes only supports this for the iTunes DJ playlist. This playlist selects music from your library to play automatically and shows some upcoming songs. You can choose a song to be next by right-clicking (control-clicking) on it and choosing "Play Next in iTunes DJ". You can also choose "Add to iTunes DJ" to put it at the end of the list already in iTunes DJ.

The next version of iTunes will support this from any playlist, through the "Up Next" feature. After playing the song you choose, it will return to the playlist you were in, even if that song wasn't in the playlist.