As a general rule, 300 Win Shares puts a player in Hall of Fame territory. It's not a guarantee, but it does merit a conversation. Here's a list of everyone at 250+ as of the end of this season.
426 - Gary Sheffield
407 - Alex Rodriguez
405 - Frank Thomas
401 - Ken Griffey Jr.
395 - Greg Maddux
373 - Manny Ramirez
353 - Chipper Jones
350 - Jim Thome
344 - Jeff Kent
327 - Randy Johnson
326 - Luis Gonzalez
325 - Pudge Rodriguez
320 - Derek Jeter
315 - Tom Glavine
306 - Jason Giambi
305 - Carlos Delgado
302 - Vald Guerrero
301 - Bob Abreu
301 - Jim Edmonds
296 - Brian Giles
288 - John Smoltz
286 - Albert Pujols
284 - Moises Alou
274 - Mike Mussina
266 - Todd Helton
264 - Scott Rolen
263 - Omar Vizquel
257 - Johnny Damon
256 - Andruw Jones
253 - Carlos Beltran
251 - Pedro Martinez