I have taken multivitamins since I was a teenager. There for a while a year or three ago I stopped taking them. During that time I noticed a diminished ability to crack. Most especially my thumb joint - my favorite crack. Then when I started taking the multis again I noticed my thumb joints were cracking again. 
Anyone else notice this?
I can crack both my elbows similar to the way tiffster does it. Only I flex by bicep so that it puts pressure on the joint as I extend my forearm out and twist simultainiously. Makes a loud, hard crack too. They will only pop once - but then I can pop them again maybe a hour later.
I do drink a lot of soda pop. Does anyone else? I have always thought it was the carbonazation of the soda that made my joints pop so easily.
None of the above for me folks! Sorry, I'm new here as this is my first post. Been a "cracker" for probably over 30 years now I suppose.
Anyway, when I pop my knuckles I twist my finger along a imaginary straight line that runs through the middle of my finger lengthwise. It is pureley a twist motion with no bending at all. Gives me a very satisfying crack and I don't have to twist very far so I never hyperextend the joint.
It has always been my "opinion" that there is no damage done to my joints by cracking them in this manner (twisting). It has always been my goal to find a way to crack my joints in way that does not hyperextend the joint. It is this hyperextension that does the damage to your joint - like pulling your finger all the way back until it pops - your finger wasn't engineered for that!
Try the twisting thing yourself - my guess is that you will like it. I do my knees and elbows the same way.