Haven't done too much research, but I know these:
-Will Leer (1:54 and 4:16 in HS) ran for Pomona-Pitzer, now 3:36 1500 PR
-Nick Symmonds (1:53 and 4:20 in HS) ran for Willamette, now an Olympian for 800m (1:42)
-Mack Chaffee (don't know HS times) ran for Williams and has broken 4:00 post-collegiately
-Bill Rodgers ran a 9:36 2mile and went to Wesleyan before winning multiple Boston Marathons
Anyone know any other elite runners who ran D3, their HS PRs, and how much they improved?