Of course a best-case scenario would be having a reliable family member that can loan me money in a pinch. I used to be able to borrow regularly from my mom and dad (always paying them back promptly, of course), but now that they're retired and on fixed incomes themselves, I simply can't bring myself to do that anymore. And there's no way I would ever ask a friend for a loan because I've seen firsthand how financial squabbles can kill friendships.
Instead, if I need to get fast cash, one thing I do is search around the apartment to see if there's anything I can sell. This could be old DVDs, CDs, books, furniture, or anything that someone else could still get some mileage out of. I then place a free ad on Craigslist and usually get a couple of phone calls within a few hours. Granted, this isn't the most reliable method to get fast cash and it's not going to yield hundreds of dollars, but I can usually count on getting a quick $20 this way.
Another way to get fast cash is to get an advance on my credit card. Again, this is not something I do without considering the seriousness of the consequences if I don't take care of the bill on time. Specifically, my credit will be ruined and I won't be able to use my card for other emergencies if I don't stay up to date with payments.
And finally, when I'm extremely desperate, I can always get fast cash from a payday loan service. I've done this a few times, but again, and very wary of the exorbitantly high fees and interest rates associated with taking out one of these loans. Still, this is such an easy way for me to get fast cash, especially since I've got a solid work history, that it's hard to resist the temptation. Fortunately, I've always paid them back right on time thus far and haven't been penalized above and beyond the usual fees.
Anyway, these are the most reliable methods I use when I'm in a bind and need to get fast cash. I think most everyone can do the same things, so if you ever find yourself in a financial crisis, follow through on one of my suggestions!