CodeRush, by DevExpress. Most consider either this or ReSharper the way to go. You cannot go wrong with either. Both have their fans, both are powerful, and both have talented teams constantly improving them. We have all benefited from the competition between these two. I won't repeat the many good discussions/comparisons about them that can be found on Stack Overflow and elsewhere.
Another alternative worth checking out:
JustCode, by Telerik. This is new, still with kinks, but initial reports are positive. An advantage could be licensing with other Telerik products and integration with them. There are bundled licenses available that could make things cheaper / easier to handle.