Bert Decker has some really fantastic tips for ending a presentation.  Decker suggests that the last three seconds of any presentation are among the most important.  His tips:

1. Don’t step back.  If anything, take a half-step toward your listeners at the end.  Don’t step back verbally, either, by softening your request to “I surely hope something…” or worse, “There seems to be a need…”  Keep saying “we” and “you” to the end.
2. Don’t look away.  Some people harken back to the last visual-aid, as if for reinforcement.  Some people look aside, unwilling to confront listeners head-on at the last words, the murmured “thank you,” or the instant of silence that follows.  Stay with them.
3. Don’t move on the last word.  Hold still for a half-beat after the “you” in “thank you.”  You don’t want to look anxious to get out of there.  If anything, you want to let people know you’ve enjoyed being with them and are sorry you have to go.  Don’t rush off. 
4. Don't raise your hands.  In our seminars, we recommend “clean and firm endings” to actually show people you’re finished.  You must “let them go” visually.  If you keep you hands up at waist level, you look as if you have something more to say.  You’re still “holding them.”  (You can see this same phenomenon in on-on-one seated conversations:  the person whose hands are up still “holds the floor” and the listener will not begin talking until the hands themselves are finished.)  In speaking, think of yourself as the gracious host or hostess as you drop your hands with an appreciative “thank you.”  That image prompts you to be warm and natural. 
5. Don’t rush to collect your papers. Or visual aids, or displays.  Stop and chat with people if the meeting is breaking up, then begin to tidy up in a calm, unhurried manner.  Otherwise you might be contradicting your calm, confident demeanor as a presenter.
6. Never blackball yourself with a critical grimace, a shake of the head, eyes rolled upward, a disgusted little sigh.  So what if you’re displeased with yourself?  Don’t insult your audience by letting them know you were awful; they probably thought you were pretty good.  One lip curl in those last three seconds can wreck 30 minutes of credibility.

Bert’s blog is one of my new favorites.  It is chock-full of great tips like these.  Add it to your aggregator.  You won’t be sorry.