+Steve Wick recently posted on his blog Tools for Teachers about using Slides Carnival for Google Slides templates.
I remember posts about this site awhile back, so gave it a closer look. Slides Carnival has a nice set of templates. I found about five I downloaded to Google Drive.
Two things stood out for me; when changing page size icons and text are automatically reconfigured so slides do not look distorted, and solid suggestions are offered on the slides themselves.
So if you are looking for some new templates to spark up your presentation, take a look at Slides Carnival.