I'm a recent C25K graduate and an Android fan, and for lack of an existing app I developed the C25K App for Android which tracks and times your workouts and lets you know when to switch from walking to running and back. There's also a fancy "Pro" application that has background mode, music player integration, custom sounds, and other goodies.
My apps enable you to listen to whatever you like, and still be motivated and focus on your running, by not having to constantly track the time. I honestly can't imagine having finished the program without it, and I'm not alone — read what some other users are saying about it.
So if you're the proud owner of a T-Mobile G1, MyTouch, Moto Droid, Droid Eris, Samsung Galaxy, Nexus One (Google Phone), Tattoo, etc, etc, and are doing the C25K plan, check out my app. Basic version is free! Pro version has a 24h return policy.
Scan the barcode below or search for C25K on the Android Market!