Haven't found any Blondie crossovers today, but D.D. Degg caught another one I missed yesterday. It was in a strip called Through Thick and Thin which, I have to admit, I hadn't heard of before.
In the Blondie strip itself, the Bumsteads are embarking on a vacation and along the way, they'll apparently run into a few more characters from other strips. I'm guessing that if any other strips do anything, they'll do it on Thursday, which is the actual anniversary of the Blondie feature.