I just started using SimpleTags last week after shopping around a bit. I really like that you can use it with any blogging tool or method (like via email or standalone programs) not just when posting from the WordPress admin itself. All you have to do is enclose what you want in a square-bracketed [tags] field inside our regular post. I’in the middle of a gradual rebuild of my site layout, so I may end up deemphasizing the tages a bit with CSS. I’ve been very happy with SimpleTags.