Are you looking for fullblood bulls & embryos or older purebred bulls and embryos?
xxcc and telos are fullblood gurus
for purebred bulls that make great cows
FR Magic
DF Midas
Poplar Hvn Smithbilt
Streamliner (Twin Creek Etulason) is a big red real world performance fullblood bull - also sire of Power Plant
Ferris Ranch Strutt (Cunia grandson) sires bigger framed, narrower, pretty females making really good cows
Pistol Pete also made some really good cows, as did his DJ Bullseye - although he was not terribly consistent
There are also some fairly well known older cow families - DMCC Beauty & Dancer families, K&A Carlene, LLND Ashley, Dejongs had a great cow whose name I don't remember right now; Wise's had some exceptional cow families ZTA Black Ruby 224X and ZTA Lucy come to mind
YC - I have friends who swear Stinger makes great crossbred cows, although people who say him called him a freak of nature - with all the clean bulls around not really sure what he offers that you can't get from a clean bull - consider your snarklies safe for the moment
knabe - think YC means Iabon and Dabla and Covino III