Umm here's the first few in no particular order that pop to mind (one line from each only, you'll have to remember the rest of the words for yourselves!)
"You are my Rovers" (already mentioned)
"Run Run, Whoever you may be"
"I can't help falling in love with you"
"Give us an R"
"What do you think of B*lton?"
"One night in gay Paree"
"Birkenhead is wonderful"
"White Army"
"Super White Army"
"Oh Johnny Johnny" (or whichever player, I guess Oh Chrissy Chrissy is the current variation)
"There's only one..." (whichever player) "walking in a Rovers wonderland"
"We ain't scousers" (not... we 'hate' scousers)
"When I was just a little boy" (okay we do)
Personally I'd love to hear the
"Tranmere, Tranmere, Tranmere"
and
"Super White Army"
songs going on for round after round after round and just not stopping, like they used to. Now they only seem to get around once and people just clam up, leaving the ones who do want to keep on singing feeling embarrassed. It's only when you get a few people who'll sing on regardless and not clam up that others pick it up and join in, but without inspiration on the pitch most people aren't prepared to do that.
Oh and one of my personal favourites, not sung as often as I'd like - "FIZZI FIZZI O Physi Physi O Physi Physi O, Physio Les Parry"