A simple question, huh. I personally do not know of an ideal fitting to use between Galv. and PVC. Forth Year gave you some fair advice. I am not sure if I argee with him 100% on a SCH 80 nipple threaded on one end as the best way to go. But, I would be a hypocrit to say he was wrong because I have cut PVC nipples and used them this way. I know nipples are available with threads only on one end, I have never used them, I have cut them.
I would not say that nipples are better than schedule 80 male adapter. Two things concern me about using a nipple cut in half since there are two different types of nipples available. First there is the injection molded nipple with molded threads. The problem with these is that the outside diameter can vary from standard pipe (typically smaller OD) and I think the glue (solvent welded) joint is weak. Second, there is the nipple made from PVC pipe with factory cut threads. All other things equal a part with moulded threads is stronger than one with cut threads. A PVC nipple with cut threads is more sensitive to cracking. This is why I think a schedule 80 male adapter is a good way to go. One step stronger (but may not be readily available) is a male adapter with stainless steel reinforcing on the inside. I try to avoid any threaded joint on PVC, and I try to avoid plastic pipe.
By the way Christopher, have you given any thought to using galvanized, the pipe you put in should last as long as what you are connecting to. And, no plastic or copper will beat galv. against shovel attacks.
Anyone have any other ideas or opinions?