Bungleweed

That should be pretty telling in my experience... I have both in my yard. My ajuga is annual and does not remain in winter months, the lavender doesn't bloom, but does leave a rather dead looking stick bush all winter long (unless I cut it back). Maybe other varieties are different??

I felt similarity as all suggestions comes from...Lamiaceae family.. so I was not so far..

Hi Rachel.. Isn't it Lavender/Lavendula..? http://en.wikipedia.org/wiki/Lavender

Ta Ra Ta Ra - Bugle!

Thanks Michelle - Sarah had it a while back - Ajuga reptans looks likely(aka Carpet Bugle or Carpet weed) escapes into lawns (used for ground cover by nurseries)

See here, looks like ajuga to me as well! http://en.wikipedia.org/wiki/Ajuga

Perennial Salvia or Meadow sage?

Lavandula

That looks like ajuga or bugleweed... :)