Hi,
Most annuals don't need a cold period to germinate. There are a few exceptions like poppies.
Biennials like hollyhocks often need a cold period.
As you already know tender perennials don't need a cold period.
Many perennials need a cold period especially those originally from northern areas as you guessed. Some perennials don't, but they will often germinate at a higher rate after a cold period than regular sowing. Winter sowing is a great method. If you haven't been over there, check out the Winter Sowing Forum. Here, I try to get my perennial seed containers out by the end of Jan./beginning of Feb. Where you are, you probably need to get them out at the beginning of Jan.
Oh, and the proper term is Cold Stratification. : )
Remy

Thanks! Funny, I thought the term was Cold Stratification, but I had no idea where I got that idea, and somehow it didn't seem right. Very helpful info. And thanks for alerting me to the winter sowing forum. I've barely scratched the surface of Garden Web, obviously. (I was thinking mostly of annuals, so it's good to know quickly that I don't need to worry about cold stratification for the moment.)
I appreciate your help immensely.
W.