I've always been a fan of Apple's "I'm a Mac" ads, especially the way they tweak Microsoft's OS and products.
I don't always understand what the actors (John Hodgman as a PC, as Justin Long as a Mac) are supposed to represent, however. Take the latest ad, where "PC" disguises himself as "Mac" to convince a potential Mac buyer to buy a PC instead. What is the real-life analogy here? That PCs are pretending to be Macs?
Here's a better one. Patrick Warburton plays a "top of the line" PC - all style, no substance.