What are some examples of interbreeding between species that are separated by 5 million years or more?
I depends a little bit about what you mean by interbreeding. In any case, my answer won't be fully satisfactory.

Horizontal gene transfer

If you are referring to any exchange of genetic materials than, you can have a look at Salzberg et al. (2001) who report 40 genes that were horizontally transferred from bacteria.

Elysia chlorotica is sea slug which is able of photosynthesis thanks to a horizontal gene transfer (Schwartz et al., 2014) 

Typical interbreeding

If you are thinking about some kind of more common type of inbreeding, then you might want to consider

mule who is the hybrid between a male donkey and a female horse. Donkey and horse share a common ancestor that is about 4.5 millions years old (according to Live Science). Mules are often sterile but some of them have been fertile (Rong et al. 1988; see also this article from the Denver post; thanks @iayork)

Platanus × acerifolia is a hybrid between Platanus orientalis and Platanus occidentalis. Platanus are a rather old genera with fossils of 115 millions years old found (from wiki). However, I don't know how old is the common ancestor between P. orientalis and P. occidentalis

There are plenty of other examples in wikipedia > hybrid but I failed to find good estimate of common ancestry for those who may have had a common ancestor older than 5 millions years but it probably exist given that the mule example is already 4.5 millions years old.