I have the C25K app fby Alex Stankovic, and I LOVE it. I think it's very well done, and I love that I can throw my own music into the app and listen while I run. You can take notes at the end of your workout to track how you feel, you can connect to facebook and post about your run... I think it's great! Definitely worth the $3, in my opinion. I'm on week 5, I've been using this app the entire time, and I can't say enough good things about it!
My mom also uses this app, and she seems to like it, too!