In no particular order I’d have:
Gronk – injury risk at the time, but probably the best overall homegrown Patriot aside from Brady.
Wilfork – they got lucky he fell to them, but he was the defensive centerpiece for a decade.
McCourty – most labelled him a special teamer only when they took him in the first round, but he’s one of the most versatile defensive backs in the game.
Slater – didn’t have a position in college yet the Pats drafted him and turned him into one of the best special teamers in the NFL. Also a superlative leader.
Edelman – same thing as Slater, was a QB in college but slowly grew into the receiver role and is now almost indispensable.
Some of Belichick’s best work has come with guys who were not drafted or cast offs from other teams too. Stephen Neal never played football before, Ninkovich was a long snapper, and there are plenty of other guys who weren’t all stars but gave the Pats solid seasons after coming out of nowhere, like Randall Gay, Dane Fletcher, Gary Guyton, Chris Jones, Ryan Wendell, etc.
Those guys are more a testament to the quality of the coaching in New England.