Recently members of my guild have been using a tool called Faster Ping to achieve better ping rates in game. My guild is a West Coast based guild, and attracts a lot of people from Hawaii and Australia, so they naturally have higher ping rates than those of us in the States. Faster Ping seems to be working wonders for them. It is not so much of an addon as it is a tool for Windows (though lots of people mistakingly call it an addon).
My first reaction to this was what thinking this sounded like something out of the mouth of Cliff Clavin. I mean, how can a piece of software impact something that is mainly due to physical limits? Well, after thinking about it for a bit, and reading up on what the tool does, it can.
WARNING! This paragraph will be the only one that contains technical content! Faster Ping works by removing the acknowledgement delay from TCP packets. This delay happens inside the kernel's TCP stack, and is a necessity for a lot of functions that go on inside a TCP stack. The other modification Faster Ping does is to remove delay in sending small packets (think anything less than a dozen or so bytes). These changes, at least theoretically, should not impact system stability if the Windows kernel has proper TCP/IP stack implementation. Okay, end technical content.