Oregon State has long been renowned for player development and finding diamonds in the rough, ad the stats seem to bare it out in this study by Emory University professors Mike Lewis and Manish Trapthi.
Oregon State finishes 2nd overall, Cal 10th, Stanford 12th, Arizona State 13th, and Arizona 15th at developing NFL talent. On the flip side, Washington State finishes last, UCLA fourth to last, and Washington ninth
This methodology can be a bit flawed, because Oregon State generally doesn't get many four or five-star recruits. However, the stark contrast between schools who do receive commits on that level (like a Washington or a UCLA, who are absolutely horrid at developing NFL talent given the quality of players that come into their programs) and the sturdy little Beavers in Corvallis is striking.
Jacquizz Rodgers and Stephen Jackson are probably the most famous examples of Beavers developing into NFL pros, but there are also a good number of defensive players like Brandon Browner, Victor Butler, Stephen Paea, Brandon Browner and Al Afalava.
Cal finishes 2nd in the Pac-12 at developing talent. The Bears generally receive a higher quality of recruit than the Beavers with regards to star rankings, but they have had unheralded high school players like Justin Forsett, Alex Mack and Mychal Kendricks become NFL regulars, so there's definitely some player development happening behind the scenes.
Stanford is next, and their inclusion on this list probably starts with Jim and ends with Harbaugh. The Cardinal have placed an incredible amount of talent into the NFL the past several seasons, with almost enough talent to fill up a starting roster on either side.
Arizona and Arizona State are on this list too probably for similar reasons as Oregon State: Not many recruits end up here. But the Wildcats have developed several NFL wide receivers through their Airraid and also have some solid defensive talent. The Sun Devils have plenty of playmakers themselves.