I tried a few of these apps but I wasn't really learning anything. Eventually, I found pianote.com and I couldn't be more happy - it's worth checking out as another option for online piano learning (they also have drum and guitar programs).

I agree not to buy an expensive piano (or keyboard). While a fully weighted 88-key instrument is definitely ideal, you can get by just fine on a semi, or even el-cheapo, 61-key keyboard.