I started a HOF rookie collection, focusing on New York (Mets, Yankees, Dodgers) players from the 40s-60s. Hit a brick wall with that and now focus exclusive on Mantle. As of yesterday, I was up to 250 different items (cards, premium photos, and coins) from his playing days.
My favorite cards that I own have to be his 51 Wheaties and, as of recently, the 60 Post Cereal.
I don't have any memorabilia that I am particular fond of. I have one autographed postcard, but it is rather generic. I do have a Yankees game used uniform (different player) that I am particularly fond of and hope to eventually display with some of my Mantle cards though.
The one that got away was a 1960 Venezuelan that went for a really good price. I was saving for an engagement ring and pretty sure she would have called things off if another card came through the mail before that was on her finger

Now that she has it, back to buying baseball cards!
I believe there are only another 22 or so items that were issued that I do not actually have yet. I don't plan to ever go after the unissued Topps test sets. Waiting for Al to adopt me and gift me his Mantles. Short of that, not ever going to happen. Not too many on my want list, but would like to pick up the following:
1. Meadow Gold
2. 1960 Venezuelan
3. 1968 Venezuelan
4. Plak Checklist
5. Yamakatzu (sp?)