Android only: The Android Market isn't much help at finding and recommending apps. Appazaar aims to work like iTunes' Genius engine for Android, but better. It recommends apps based not only on what you use, but where you're located.
So just like iTunes' Genius feature, Appazaar watches what you use on your phone, compares it to what other Appazaar users with similar tastes have installed, then suggests you might like some of their apps too. Right off the bat, it suggested the PDAnet tethering app (which I've purchased, but don't have installed right now) and the Concerts add-on for my favourite music player, Cubed. Appazaar provides these apps and does its monitoring through a home screen widget, and you can set the app to blacklist certain apps if you get sick of a particular persistent push.
What Appazaar also claims to do, which requires further testing and broader usage, is to monitor where you are at times and use that to figure out how you're using your apps. It supposedly takes your location into account when recommending apps, so that likely means local apps of interest but also some context.
Appazaar is a free download for Android phones. Scan the QR code at the link and tell us how it does for your own recommendations in the comments.