If you take the time to watch Old Faithful erupt, you might as well take some time to wander around within Upper Geyser Basin. Old Faithful sits on the edge of Upper Geyser Basin, and there are plenty of other geothermal features to see, including other less famous geysers. If you are really into it, then you could hike about a 5 mile loop that starts next to Old Faithful, wanders through Upper Geyser Basin down to Midway Geyser Basin (yeah...there is also a Lower Geyser Basin...but we did not visit that), and then comes all the way back to Old Faithful. That is what Tammy and I did.
One neat thing that the National Park Service did was put little signs up to tell you the name of the geothermal thing you were next to. I tried to take pictures of the sign when I took pictures of the thing, but, alas, I was not consistent. Sometimes I took a picture of the sign first. Sometimes I took a picture of the thing first. Sometimes I took no picture of the sign at all. So, what I ended up with was a bunch of pictures for things whose name I am not too sure about. [Edit: While fixing this post to point at Flickr, I was able to identify what was in the first and third photos. The top photo is of Belgian Pool. The bottom photo is of Spasmodic Geyser.]
Whatever the name of these might be, they are pretty interesting looking. The bluer the color, the hotter the water. The more brown, orange or yellow, the cooler (or "less hot") the water. All of these are located in Upper Geyser Basin.