Obviously, there are exceptions with some pitchers (for instance, a pitcher I played with growing up was hitting 60 mph in 16u ball but then kind of plateued). But here's an opinion to start things off... 

The Women's College World Series blows me away every year. I played against some tough pitchers, but the teams that make it to Oklahoma City are on a different level. For the past few years, many of them have been Olympic team material. They throw incredibly fast.

I've heard it said many times that the top pitching speeds from 42 feet away for college softball equates to somewhere around 100 mph fastball from Major League baseball's 60 feet and 6 inches. I believe it. Especially standing in against Jennie Finch--her stride off the mound takes that 42 feet down to 38 by the time she releases!

I know University of San Diego has a team as well as UCSD. Historically, UCLA is the dominant college team in Califonia and, for that matter, the nation. They have won the Women's College World Series 10 times (the most of any school). Cal, Fresno State, and Cal State Fullerton all have a tradition of having very strong programs.

But there are a too many schools out there that have softball programs to list. California has been a long-time leader in fastpitch (but the rest of the nation is catching up). It'd be cool if you caught a game. The girls out there can play!

We had the radar gun out at pitching practice earlier this week.  My 13 year old daughter is topping out at 63 mph.  Danielle Lawrie, who throws for the University of Washington Huskies, is her favorite pitcher right now.  We got to see Danielle pitch twice last season -- once in a good victory over Stanford in Seattle, and once when the Canadian National Team was in training.  She's a great role model for the younger Canadian pitchers!

"My 13 year old daughter is topping out at 63 mph."

Time to get your gun calibrated.