It's no surprise, but there aren't too many true medical apps for Android right now that are free. You can purchase medical references, but the Android Marketplace is not full of feature-rich medical apps that can be used by physicians and other health care professionals. QuantiaMD is a great free medical app, but it's not near the top because it's being pushed down by consumer health apps. Plus, you need to be a registered health care professional to access QuantiaMD, so you won't get any consumers "testing" this medical app.
Now that Epocrates has their app on the Android Marketplace (still in beta), it won't be long before this becomes a top free medical app. Health care professionals all need access to a drug database. Plus, the pill finder is a great feature that any health care professional can use to help patients identify their medications.
I still remember the old days of the Palm Pilot when Epocrates dominated those devices. Every physician and medical student who had a Palm Pilot used Epocrates. Pharmacists and pharmacy students used Epocrates. Those were the days of grayscale screens. The original Palm Pilot didn't even have a backlight.
Now, we live in an era where smartphones are gaming devices and video players. They hold gigabytes of storage space and essentially function as mini computers with fully-functional mobile web browsers. Smartphones are now becoming a GPS navigation system for the car. They're becoming our pocket cameras. We can't imagine leaving home without our smartphones.