What's a Nickname of What, and Where'd They Come From?

I found two lists of nicknames this morning:

• "Nicknames"
  Genealogy World (September 7, 1997)
  • It's a simple table of nicknames for names from Aaron to Zepaniah, and including Penelope, Pocahontas, and Waldo.
  • There's no discussion or explanation of any of the pairings, and I'm a little dubious about the table's accuracy.
  • For example, Oswald is listed as a nickname of Waldo. Sure, they're both Germanic names, and have "wald" in them - but "Oswald" is a name in its own right, from way back.
  • Still, I had fun reading the list. Maybe you will, too.
• "Nickname Names for Baby"
  Think Baby Names (© 2004-2008)
  • "103 Nickname names for boys. Listing Nickname baby names 1-10. Archie, Art and Bert are popular Nickname baby names. Aad, Abbott, Ace, Algernon, Amerigo, Aspen and Bern are uncommon Nickname baby names. Click on each Nickname name for details and [variants],...."
  • Whoever put this resource together researched the topic. Click on a nickname, and you'll find more information. For example:
    • "The boy's name Lapo \l(a)-po\ is of Italian origin. Nickname of Giacomo.
    • "Baby names that sound like Lapo are Lippo and Loeb. Other similar baby names are Lalo, Lary, Capp, Cap, Pipo, La-, Laroy, Lacy, Ladd, Lad, Lacko, Lake, Lallo, Lale, Lane, Laud, Leo, Lino, Luano, Ludo and Nap.
    • "Lapo is a very rare male first name and a very rare surname (source: 1990 U.S. Census). Displayed below is the baby name popularity trend for the boy's name Lapo. Compare Lapo with related baby names.
  • This is, I think, a pretty good resource: at least as a starting point for researching a nickname.