If you're entertaining in your home in a stand-up, mill around style, you may want to serve foods at standing-height so guests can pick things up as they visit. You don't necessarily need a buffet, though. Here are some other ideas for standing-height surfaces to serve from:
Windowsill: If you have deep ones that are high enough, this can be a beautiful place to place party food. Bonus points if the window is located where all of the action is. Just check out the example from Mike*Laura in the image up top!
Countertop: This might be a bit out-of-the-way if you have a closed kitchen. However, it's a very commonly-used surface for party service when the kitchen's open. Islands are great because guests can help themselves from all directions!
Drafting Table: This is a bit specific to artists and designers, but if you have one, it can come in very handy when entertaining. It saved us in our small apartment!
Fireplace Mantle: Could be a bit high, but again - this surface has saved us time and again. We have often just placed glasses, plates, and napkins up there for people to pick up and food elsewhere nearby.
Stovetop or Sink: Just put a great big cutting board over it and it's a buffet!
What unexpected standing-height spots have you used in your own home when entertaining?