While there are literally dozens of options out there, both commercial and open source, we use Eagle at Adafruit for all of our PCB design. It's just kind of become second nature to hammer out boards and parts in it, and once a tool becomes 'invisible' to you, it's really hard to be persuaded to change.
Like everyone, we've had to plumb the depths of Google, dig into obscure posts from long dead servers, and sometimes just fire off a board and see what happens to learn the ins and outs of Eagle.
We hope you can get a head start doing things the right way yourself with this tutorial, though, and avoid some of the head scratching we had to go through ourselves!
So ... grab your mouse, fire up Eagle, and follow along as we create a simple footprint from start to finish!