There are two canonical pronunciations:
1) You Rain Us or Your Anus
2) Urine Us
Generally, if I am giving a public talk to young people and teenagers, I use the scatological pronunciation. If I am giving a talk to an older audience, I opt for the more conservative 'Urine-Us' pronunciation. When talking to other professional astronomers, or when I overhear them talking to themselves, I hear both forms being used.
Purists often draw from the greek language the pronunciation
Ooo Ron Ooos
where 'Ooo' is pronounced like 'Oooo what a yucky roadkill!' But this always strikes me as sounding a bit too high-faluting.
I think that columnist Dave Berry could have some fun with this, don't you think?