Android phone not recognized when connected to Ubuntu, by 'adb devices'
Had this very issue earlier tonight myself.

The 51-android.rules needs to be world read-execute, and it's probably best to run service udev restart (or reboot) after changing this, then re-plug your device.

If it still doesn't work, double-check the vendor ID you've supplied; with your Android device connected, run lsusb. HTC also use the vendor ID 18d1 on newer devices.