I'd recommend that you write something personal and interesting to everyone. Read their profiles and tailor the e-mail specifically for them, responding directly to things in their profile. Don't use canned responses that you just cut and paste in. Also, use spell check, write coherently, and proof the message before you send it.
I had good success a few years back before meeting my current GF, who I met online, and a number of the women I went out with commented on the fact that I wrote specifically to them about certain things in their post. Women also care a lot more about spelling ang grammer.
I also have a number of female friends who have commented on the cut and paste thing where they got the same exact message from a guy more than once, or a friend of their's got the same one as well.
Aside from that, be creative. Witty and funny!