We are doing Pebbles & Bam Bam this year.
(hopefully)
There are lots of cute costumes out there.....several YTers have costumes they sell and there is always Petedge and Ebay. (And our Petsmart had some, but is already sold out of all the smaller sizes.)
Last year we saw one person that made a "doggy in the window" that was very cute and another lady dressed up as Sandy on Grease and her dogs were the Pink Ladies and the Thunderbirds.