Acceptance With Displeasure. It's possible that your boss won't take immediate action like the reaction above__but will make it clear that he or she isn't exactly happy about your resignation. Maybe, for example, she'll mutter a curt, "Thank you for letting me know," followed by two weeks of obvious displeasure or denial that you're leaving__through gruff comments ("You know, you're really leaving us in the lurch") or a refusal to interact with you more than absolutely necessary.
State Your Intent. The whole theme of your resignation letter is the statement that, well, you resign. You don't need to play coy__the time has passed for you to fish around for a counteroffer if it's gotten this far. At this point, you've made your decision to leave, and this letter needs to reflect that.