Honestly, I think some of the later gold commemoratives are extremely cheap. I just purchase a proof statue of liberty gold $5 commemorative dead on at melt value. AGEs and basically any other gold coin usually have at least a %10 or so premium.
Liberty Head Nickels as most are very worn out. Probably not much collector interest. ( I do own a bunch though )
I'm very suprised to see Walkers come up in this discussion. They are my favorite, and I know alot of other people love them as well. I think modern business strikes are very overlooked, but I think the reason for that is good. I also agree with the people that mentioned the Roosevelt dimes.
I'd have to go with odd cents, 1/2, 2, 3, half dime, 20. It seems more often than not that the only interest in them is to have one for a type set, but seldom does someone attempt to build a complete set.