100% of the time that I've actually done something to impress a boss is definitely to show an initiative on getting things more efficient. Do not wait for your boss to give you instructions, just start branching out an experimenting within a reasonable level to make your life a little bit easier.
Some things you should think of, for example, is your release procedures. Find something that's taking you 1 or 2 hours and figure out how to bring it down to 15-30minutes.
If you're using C#/ASP, you're probably using .NET and the CLR. If that's the case, take a look at learning something like python and find ways to embed IronPython for an interactive console to make really cool projects come to life.
You can definitely find creative use of your time if you just step back and analyze what you're working on and think of ways to make it more efficient.