Hi Scot,
Have submitted a few myself to:
http://www.goarticles.com/author.html
http://www.amazines.com/
http://thephantomwriters.com
http://www.ezinearticles.com/
If you're not sure which is more popular, you could compare them on alexa.com's traffic rank tool - not by any means infallible, but should give a general idea of which article site is top or gaining in popularity and therefore audience/distribution figures.
HTH,
D