When was the last time you traveled? No doubt you've noticed the heightened security and 311 measures that take place now. Basically, restrictions on what you can [3 Oz toothpaste] and can't [nailclippers, tweezers] bring on your carryon bags have been in place for a while now.

As you can see from the image I took from the official Transportation Security Administration website, you can have liquids/gels in 3oz containers: this does NOT mean you can take a 6oz bottle of something that only has 3 oz or less remaining! Kevin tried this, it doesn't work! :) You are permited to take one quart-sized, clear plastic zip-top bag to place your liquids in. If you want to be fancy, you can buy some clear jars/bags from this neat 311 travel gear site.
I don't do the 'check' baggage thing because I'm too paranoid that my luggage will get lost, stolen, broken into, etc etc. I'm also not patient enough to wait for my things to get thrown off of the plane, slammed onto the conveyor belt, and then roll down the dispenser into my loving arms. If you simply have too much stuff to haul and you need to check, you should look into these neat locks. They are TSA approved! Basically, it's a luggage lock that the security folks at the airports can get into, but airport employees and hotel bellhops can't!

I think I'm going to invest in a couple. My mom likes to check bags when we go to El Salvador and they tear your stuff up! It gets to you all half-open, panties hanging out, and whatnot. These locks look pretty neat, it says they have 'global' ones, which means that international airport personnel will be able to check into your things, too.

Update: I bought one! Cost me about $10 at Macy's. Yay!