Scott Kirwin at Dean’s World has a great post you should read on his conversion from a Democrat to a Republican. Here’s a little of it:
I broke with the Democratic Party after Sept. 11, 2001, when the President prepared for war in Afghanistan and the anti-war Left summoned Jimmy Carter, Michael Moore and Ted Kennedy from the 9th Circle of Hell. The Democratic lurch to the Left after 9-11 was so hard, so anti-populist, that it got me to thinking deeply about what that party means and why it exists.
Make sure to read the whole thing.
On a personal note, I made the switch from Democrat to Republican back around 1994. You can read the short version here (scroll down a bit for the conversion part as a lot of that is a post telling you who I am). The long version will likely be posted at a later time