The best part about original art--particularly sketches--is how much they seem to convey a snapshot in time. I think they're like photographs, but done by hand. They have an immediacy and looseness that captures a particular moment in time. Even when they're presented as gifts or purchased somewhere, you'll always attach a memory to it. I'll never forget seeing a collection of Don Barchardy's drawings in London years ago. They were all the same size (24 x 36 ish), and there were dozens of them. You could imagine them being presented to their famous sitters/subjects after Don was done.
One of my own prized possessions is a little midcentury sketch that was given to me as a wedding gift. It hangs in my bedroom and I always think about how/when it was created and the people involved.
I've sold my own sketches to clients before (they're a good 15 years old, which kind of makes them vintage ;) and I also recently gave two away as gifts. It felt good to give something that I had made myself:
So go out there and make your own art, or find something similar. I think organic pieces with high contrast can really balance out all the photos, posters, and other art in your space. If nothing else, you'll have a great story to tell your friends and visitors.