Watch the String Bending online guitar lesson by David Grissom from Open Road Guitar
Along with vibrato, string bending is one of the techniques that can really give the guitar a vocal quality. Take a look at bending with the third finger, this ties in directly with the hand positioning I've been discussing previously. My thumb will be over the top of the neck and I'll use my first and second fingers behind my third finger to give more strength to bend. After that note I will add in vibrato as well as it makes it a much more interesting and soulful note. I am getting that control from the thumb and the two fingers behind my third finger. The third finger is the main finger I bend strings with. Next we will bend with our first finger. This takes some time to get together as it requires a lot of hand strength, stick with it - it will come. As you can see from the video I will bend in either direction with my first finger as I feel it gives the note a little bit of a different sound. I also use my second finger quite a bit to bend. I like to do this with inside chords like you will see in the example where I bend the 3rd to the 4th for a pedal steel style lick. I would suggest experimenting with bending with all fingers. Personally I don't bend with my fourth finger all that much but when I do I reinforce it with my other fingers.