Stay at the "buzzed level" and then order a glass of water with everyone of your drinks. Don't order your next drink till you finish the water. If you stay at one drink every 30ish minutes, you can drink all night long, stay loose, and you'll have nothing when it comes to a hangover the next day.

+1, I did this for my leaving party just before I went travelling round Oz, and It's an awesome trick to use, we were drinking for a good 10 hours, and I felt (almost) sober.