Never mind, Rob Markham may be in a bad day...

Well, mea culpa, there is effectively some other interresting ADC with I2C interface.
I've looked at the MAX1069 datasheet and it's a very good alternative for PCF8591.

In the recent past, I've looked for other I2C ADCs without success. The trouble with PCF8591 is that it's only an 8 bits ADC and I was needing 10 bits and next the cost is a little high here in France. I've not checked the MAX1069's price.

I hope Rob Markham will tolerate that my answer to Michael Kern was wrong although I was saying that the answer was from "my mind"... We're all do our best to participate to the forum and the quality of the feedbacks are coming from what everyone is able to share. I'm happy to see that finally it's operating as Rob Markham has completed my post.

Regards
Stephane