It doesn't matter if the party you're hosting is a few people huddled around a sad bowl of chips, or a hundred people sipping champagne and watching rented swans strut about the lawn of your estate - the cheapest and best way to leave a warm, lasting impression is to greet guests at the door.
Anonymous, drunken dance parties are cheap to come by - that's what frats are for. Anonymous, drunken guests are a whole lot likelier to raid your medicine cabinet looking for pain medication, and walk off into the night with bottles of 50-year-old scotch. So do what you can to greet everyone and let them know you are so glad they could make it. Practice your best super-excited-to-see-you! face.
Talk to new people as though they are your future best friends. Take their coats and let them know where their coats are disappearing to. Get them a tasty beverage.
If people show up before you even started making the guac, consider delegating - it's a lot less awkward for two or three people to make themselves useful in the kitchen than it is for those same two or three people to try and make small talk in a room devoid of guacamole.
In the halcyon days of yore when Polaroid film was only a dollar a shot, I used to take pictures of every guest and create a photo gallery on the wall. Not only is it a constant conversation piece throughout the party, it helps guests avoid having to ask, ummm, what's your name again? And the next day it helps drunken hosts who can't remember who the in the world was at their house last night.
These days you can invest in an Instax camera from Fujifilm - which takes stylish little shots the size of a credit card, and prints them out instantly. Or snap shots for later with your digital camera. For the look of a polaroid without the price tag of the Instax (or the satisfaction of an image you can hold in your hand and slap on the wall), you can use the Shake It app for iphone.
If it's your special day and you rented a larger venue and you just don't want to babysit the door all night, consider asking friends to do the greeting for you - or hiring someone to take pictures. If you're leaning on your friends, pair them up so they have someone to chat with, and give each volunteer a half-hour shift - then their stay at the door seems less like drudgery and more like a little party-break. I also highly recommend having a guestbook - or a photo guestbook - at the door; even if you aren't able to talk with each guest one-on-one, they'll know their presence mattered, and you'll have a great album to look through the next day.