We usually invite about 30 people to our parties. We always recommend that people carpool, but of course that almost never happens.

We do let people park in the front yard, driveway, and some do line the street as well. Not ideal but it works. My neighbors are also aware that I throw a annual Halloween party. At my last house though, just to make sure this was cool with the people I lived next to.. I would go over to their house and let them know that we were having a party and would be having our guests park lining the street. It was always appreciated that we would inform them so they didn't awake in the night wondering what the heck was going on. An added bonus for us was that because we took that route, no one would call the cops on us for noise.
Last year we ran into a problem with our guests parking in the neighbor's yards. We had to make people move which wasn't welcomed very happily. So this year we are going to park our cars on the border of the yard and direct them to park in between us. We think it will go over much better. Unfortunately, for those of us who don't have much land or space there isn't another solution that I have thought of. Hope this helps a little bit!