My wife and I do this all the time!
Our favorite is when she talks a big dildo (John Holmes, BAM, or even bigger) in her vagina, while I penetrate her anus.
She also likes it when I insert a dildo or vibrator in vagina while using my own penis at the same time. Depending on her mood, the size of the vibrator varies from normal to good sized to very big.
As 55 plus said, it is hard to recommend different models since each person is unique. If you had told my wife and I we would be playing with the sizes of our current toys a few years back, we would have laughed and laughed...now we can't get enough.