A friend told me it was this all-in-one SEO pack but I'm not sure if that's the same thing I am asking. http://wordpress.org/extend/plugins/all-in-one-seo-pack/
There's actually quite a few, check out this list of the top ten social bookmarks to find one that best suits your needs.
Sociable (listed above) is also very good. I prefer to use that as opposed to ShareThis, but ShareThis also gives you stats.
Social Bookmarks seems the most legit. After researching it though I am surprised that out of all the sites it supports Twitter is not one of them. I thought they were a standard for this type of function and I'm pretty sure I didn't see it on the LIST. That is one the sites my client requested for her website.