I have an assembly of mismatched computer accessories on my work top; and I love it. I have two different monitors, an old beige keyboard from bygone era, a Wacom tablet with a pen input device, and a mouse that came as a free gift. The assortment looks quite charming in its own way.
It all started with wanting to learn more about Photoshop from video tutorials. I took an old 15" monitor from our server. My son, who I must admit is much more adept at computers than I am, gamefully set up everything for me. My computer's motherboard already has 2 monitor sockets, so I did not have to spend a penny. I can now watch the tutorials "live" while following the steps on the other monitor. I have tried this out and it is really a breeze.
As for the server, well I had it connected to the monitor of the computer next to it (two CPU's to one monitor). The server is seldom used directly, but when a monitor is required, I just need to press a button to switch computers.
Here's a picture of my workspace.