This answer varies depending on who you ask. If you have film, yes, of course, include it. If its not right for that particular coach, they may ask you to re do the film, send full games, etc.
The best emails are concise and include all pertinent information, swimming times, your height, how long you have been playing, your coach's information...all the basics.
If you want to set yourself apart, do some research on that particular team. Hey coach, I saw your game against ABC, your center really is good! Or I see you are losing two goalies this year, how many are you planning on bringing in?
Try to set up a visit to the school. When are junior days? When does the team have a big recruiting weekend where they bring in lots of recruits (i.e. your teammates for the next four years)?
Also, keep a very detailed list of who you have emailed, and what stage of contact you are in with each coach. You should be in touch with enough schools to where you need a list to keep everything straight.
Please do yourself a favor and make sure the coaches name is spelled right...and that you are emailing the correct school...yes, we get emails for other coaches all the time. It means you really aren't interested in our school...