Months ago for me, it was my boyfriend's finger but I decided I didnt really like it (it really made me need to pee!) so we havent done it since.
I wouldnt mind trying it again with a plug or beads - something that isnt meant to move around as much would probably be more comfortable. I've made a wishlist now with things I might try if someone else bought them for me, the OH might find it some time.