Apps for Hobbies

My son has been drumming for 3 years now.  He was only 7 when he started but he has a lot of natural talent and has kept with it.  We just recently started him on drum lessons and I think he is doing well.  His drum teacher wanted him to use a metronome to practice his rudiments and I just happened to find an app on my iphone that was a metronome.  How awesome is that?  I am all about finding inexpensive ways to fund our hobbies.  Any ideas? I bet we could use abt electronics coupons to buy drum accessories online.  Amazon takes them and usually you can spend over $25 to get free shipping.  Sounds like a win-win situation to me!