Shot in the dark here, but you've probably got some apps constantly using GPS, wifi, 3G, etc. Or maybe, if you're using a combined inbox, it's taking up too much battery pulling emails.
I recently set up my friend's email on his new Droid as he didn't want to use a new Gmail account. I initially set up his combined email accounts (all of 4 of them) to check for new emails every 5-10 minutes. Over the weekend we were in Vegas and his battery was dead a long time before mine and we had been using our phones the same amount. So I changed his settings to have email pulled ever 30 mins. and his battery life has been greatly improved. I s think I set his work email to get pulled every 10 minutes and personal to get pulled every 30-45.
...or use Gmail like you should be anyway.
Hope that helps.