Part of the difficulty is in defining "rare". For some people, "rare" is any coin you have to pay more than $10 for.
There are some books out there along the lines of what's been suggested; books like
Milestone Coins that list the 100 favourite coins of the author or authors; some are "rare", some not. All are popular - some even more so, now that book is out. I sure haven't seen a silphium coin of Kyrene available for decent money since they were listed in that book.
