Swingin' Metronome
The rhythm most commonly use in Blues is that of swing-eighths... it's the foundation of our shuffles, swings and slow blues. It can be a challenge to feel the swinging rhythm, especially when studying a new passage of music... but of course we have technology to help us out.
The swing rhythm is triplet based... 1 2 3, 1 2 3, 1 2 3, 1 2 3, etc. Swing uses the 1 and 3 of the triplet, leaving 2 silent or held over from 1. Another way to think about it is that every downbeat (foot is down) receives 2/3 of the beat and the upbeat (foot in the air) is slightly later in time than we would instinctively would place it and is worth only 1/3 of a beat... 2/3 + 1/3 = 1 beat.
Visit http://www.facebook.com/bluesharmonica for a picture of my simple iPhone app called "Tempo" to see the one button setting to swing the rhythm. Example 1.8 in Solo Harmonica Study 2 is a great example to study since it's almost entirely constructed of swing eighth notes.