I find "Band in A Box" an essential for teaching and for practising.
http://www.pgmusic.com/
It lets you enter chord symbols, pick a style and tempo and you can have a decent backing track for practising along with in seconds. I use it to enter chord progressions to practice improvisation, and to make quick tracks for students to play along to.
One the best programs ever made! It comes with some guitar lessons and a great ear training program too.
You can also download most of the Real Book for free (if you don't know - that's the book that contains many of the jazz standards that every jazz musician needs to know) in Band in a Box format.
It is well worth buying!
