I love doing hip-hop covers. I've even got a project which
mostly does rap covers of country songs about partying, drinking etc. That kind of thing could be a good option with the acoustic guitar and female singer. I've also heard someone else do a rap version of Willie Nelson's "I Gotta Get Drunk", that one works well. You just gotta do it at a fast tempo so the lyrics flow properly.
Some general stuff that will probably also apply if you want to cover rock or pop songs... As you can hear from the tracks on our Myspace, we speed up the songs quite a bit sometimes, so you gotta pick something that's not too short in the first place. We often end up doing medleys and borrowing lyrics from other songs to make more verses to make the tracks longer, but in your case you should just probably pick one longer song to make it easier.
Also we often will play something in a minor key even if the original is major - not sure why but it just sounds better that way a lot of the time.
And a few easy possibilities that would work with your lineup:
Charlie Robison "Good Time"
Roger Creager "The Everclear Song" (we stole a bit from this for a verse in another track)
Robert Earl Keen "Feelin Good Again"
Richard Thompson "1952 Vincent Black Lightning"
Tom Jones "Sex Bomb" - not country, obviously, but we're working on something based on this song now
