Most clubs give out "VIP" Passes/ Line Passes. These passes are either free or reduced admission and or line passes. Most are good up till a certain time. Most expire at 12:00 some go until 12:30. Most require that you make it into the club by the time alloted on the card.
Not be in line by. Some also free before a certain time half price after. The line passes mean that you will get into the VIP/ Hotel guest line.
Not that you will walk straight up to the club and get in. Most are not good on holidays or special events. They can be found everywhere in Vegas. Mostly places affiliated with the nightclub scene. Fashion and music stores, Cab drivers, timeshares, hotel concierges, valets and rental car services. Some hotels let their hosts and promoters hand them out in the casino. The best place to get them is from local promoters and hosts, WHO WORK FOR THE CLUB.
The promoters for the clubs give them out for free because they get paid by the club. Anyone who is selling them does not work for the club but that doesn't mean that the passes are not good. These passes are key if you are just looking for somewhere to go and don't want to spend a lot of money.
Some hints with passes: Don't go 5 min before the passes time ends chances are there are a bunch of people with passes as well. Ask the promoters questions. sometimes the passes may only be good up until 12 instead of 12:30 if its the clubs busy night. Call the club if you have any question about the passes.