Build and install without run in Xcode

You can drag and drop the built app (in your project build directory) into the Applications list of your device in the Organizer window.

If you're not quite sure where the built app is (the project build directory):

Xcode → Preferences → Locations tab → Derived Data will show the location.

There's more information in this question: Xcode 4 - build output directory

Things have changed a little since this answer...

For simulator, you can drag/drop your recently-built app product from the Products folder in the Project Navigator straight onto the simulator window.

For a device, drag and drop the app product into "Installed Apps" when viewing the device in the "Devices" window.