Catcher Mom:
Check out the "Information Letter" template in the "Recruiting Tips" section (linked below).
Recruiting Tips for Players & ParentsIn my opinion, most coaches want your son's information in a simple, straightforward form. However, this doesn't necessarily mean that you shouldn't personalize it if your situation warrants it. For example, a reference to the college's current season...to show that your son is interested enough to follow their results...can help your introductory letter stand out.
Don't send videotapes unless they're requested. Better to attach a summer schedule, giving them the ability to be on the lookout for him in person.
Finally, it's always better for your son to be the one who's directly involved in the correspondence process. Coaches have a knack for determining when the parents are doing all the work; and they like it much better when the player shows the desire and maturity associated with their direct involvement.
Best of luck to your son!