Congratulation, cigars all around (okay, a little early for that.) My youngest is 12 (oldest 21 and in college) so I've forgotten most of what will help you right now. I will say make sure and support your wife through the whole pregnancy and delivery, she has the hard part. And change diapers and help with the feedings, no matter how much your male friends and relatives give you s**t about it. You'll get back much more than you put into it.
I'll second Kelly's advice, enjoy every minute you can, because in what will seem about a year, adult time, they'll be asking for the car keys. Remember when you were a kid and summer seemed to last forever? I've now got a 21 year old son in college, a 16 year old daughter who wants to go Naval Academy or NROTC and a 12 year old son who's smarter than me. How did that happen, since I only feel about 25 myself?