Well the one that immediately comes to mind is Technique Tuesday. They do a lot of sentiment stamps.
Of course there are a lot of stamp companies but the Ali Edwards, Technique Tuesday ones are what I think of when you mention sentiment.....
Love Ali Edwards!
stopped buying because I don't do cards - only layouts. And there is little chance I'd use the same sentiment or saying on two different layouts. So I switched to rub-ons - they are awesome, one ot two packs is enough, and way cheaper most of the time.