Chic - Good Times: a great Bernard Edwards bass line that's a good workout for both hands. Clean fingering and rhytmic accuracy are the key to nailing this ostinato.
And for something a little earlier, I sometimes warm up with one of the earliest and most famous bass ostinatos ever, Pachelbel's Canon in D major, composed in the 17th century. For 4-string I transpose the low D up an octave. http://en.wikipedia.org/wiki/Pachelbel%27s_Canon