Reading the Roger Bernadina thread, it sounds like a lot of people on this site have a lot of Willie Harris stories.
I didn't follow the Nats when Willie Harris was playing in Washington, but I grew up following the White Sox in Chicago, and we had Willie Harris from 2002 to 2005. I remember he was nicknamed "Broadway" in the Orioles organization (where we got him from) because he was going to be a star. But in Chicago he was mostly nicknamed "Wee Willie" Harris for his size.
My favorite Willie Harris story comes from early in the 2005 season. This was one of the least productive seasons of Willie's career, and he was sent down to the minors. When the media interviewed him after this was announced he said "you have not seen the last of Willie Harris."
They were right. He made the postseason roster as a pinch-runner, and in that role scored the winning run in Game 4 of the World Series, giving Chicago its first MLB championship since 1917.
Willie Harris had an amazing run early in the 2003 season - I think he hit .400 in April and was still well over .300 on June 1. Overall, though, what I remember most is that he was very popular among casual female fans who thought he was cute. If you counted only the sale of pink jerseys, his jersey may have been one of the most popular.