I found a nice site HERE
The first half of this circuit is used to bump up the voltage from a 12V source so that you can charge three cells. I have a 14V power supply so I was able to omit this part. This really makes the circuit simple. The only limitation with this circuit is that it does not have a cuttoff at the end of the charge cycle. I just keep an eye on the lamp. When the lamp goes dim, you know that you're in the second stage of the charge. From that point, I just time it so that the batteries charge for another 15 min.
You can get really fancy without much more effort/cost by using THIS
chip. It's a single chip lithium battery charger with built in smarts for ending the charge cycle. It even does low voltage recovery of cells that have been discharged too low. Page 12 of the spec sheet has an example of a simple circuit using this chip.