The TP roll and 2 dollar are the main ones I see going around, though I have seen a few others. Most of them are pretty similar to the quarter challenge where you just try to compare to a set object, dollar bills and coke cans are pretty common in this respect. One of the more interesting one's I've seen is to try and see how far you fit into a fully unrolled condom (ideally a large size) , if your dick touches the end you win, and you get bonus points based on how tight it is.
I can't say I pass most of these tests but it's still a lot of fun to see how I stack up.