This is actually a topic that's really dear to my heart...I do a lot of PG cursing because it irritates my husband so much
He says "Jesus Christ" all the time, which I do get a bit sick of hearing, so I like to come out with the most childish substitutes I know, like "Cheese 'n' crackers!" or even "Peas 'n' rice!"
Another good one-- I picked it up from Donald Duck comic books --is, "Gosh all fish hooks!" I use that a lot.