In recent memory, I can recall Uncle Chuck (Journeyman Stallions, FL), King for a Day (Irish Hill & Dutchess Views Stallions LLC, NY), and Demarchelier (Claiborne Farm, KY).
After doing some light searching, I also found a few more.
- American Pastime (Swifty Farms, IN) GS3P
- Dolphus (Darby Dan Farm, KY) G3SP
- Lost Treasure (Hill 'n' Dale, KY) G3SP
- St Patrick's Day (Journeyman Stallions, FL) G3SP
- Union Jackson (Sequel Stallions, NY) G3SP
- Venezuelan Hug (Mill Creek Farm, NY) G3SW
None of the ones on the list have won or placed in a G1 or G2. There are WAY more stallions in FL that have been non-graded stakes winners/placed (or less), but I omitted them because I didn't think they were relevant to the question.