There is, but it appears the independent developer who made it hasn't updated it in a couple years, so it may have issues with WordPress installations newer than v3.0.5.
http://wpejunkie.com/
Aside from that option, it's quite easy to simply copy the ready-made button codes we provide and paste them into your WordPress site, especially if you use the Raw HTML plugin to help ensure that WordPress won't mangle the codes after you paste them in. See this help page for further details and tips:
http://www.e-junkie.com/ej/help.site-blog.htm
