There are several Couch to 5k apps out there I think. I use this one Cto5kapp
. I like it because you can set it to play with your own music and have it just chime and say "Run" or "Walk" when it's time to switch. I think it cost $1.99 when I got it but now it looks like $2.99.
Couch to 5k has actually been around for awhile, since before apps, so you can get all sorts of info at these sites, including the chart that shows the run/walk intervals. There are also threads here that discuss it.
Cool running C to 5k page
C to 5k plan
(I send my students here because it's also translated into lots of different languages! And at the bottom of the page there are links for podcasts with all sorts of different music or motivational stuff.)