Not too long ago I tried something on my wife and much to my surprise she had the best orgasm I think she has ever had. What I do is while I lick her clit I insert a finger into her pussy and bend it down slightly applying a little pressure. After a little bit of that when I know she is really starting to feel it I place my thumb (from the same hand) against her asshole and apply a slight amount of pressure there. It's almost as though I am trying to press my finger and thumb together. Sometimes instead of my thumb I will use my index finger from my other hand and will insert it. She seems to enjoy that a lot. The first time I tried this she had a very strong orgasm and each time I have done it since she has always had better than her average orgasm.
As a side note..........Since I started doing this it seems as though she is more open to anal stimulation than she was prior. I have always wanted to have anal sex and we have tried but to no avail, it was too painful. I don't have a problem with that as I would never want her to do anything that was painful just to please me but about a week ago as I was pressing my cock against her ass I thought I was going to make it in. I started to enter but before I got too far she needed me to stop. It was the furthest I have made it so maybe I am onto something here
I also like to have mine fingered slightly. Years ago I had a friend with benefits that I used to have sex with regularly and she enjoyed using a vibrator on my ass. I was into having her penetrate but let her rub it with it and I enjoyed that as did she.