There's a lot in common between HP and LotR. A lot more than just the fact that they're dealing with a "dark lord" who would best remain unnamed. Aside from his name, I think it's neat that the dark lord is vanquished at the very start of the story, then exists with a supernatural presence (an eye and a vapor), then gains strength again, before ultimately finding defeat.
Here's a link to the mugglenet page comparing HP and LotR... some of the things are quite a stretch while some of them are really odd connections.
http://www.mugglenet.com/funlists/hpvslo… The list is quite old, so there's probably many more connections from the later HP books.
I don't know if you've finished the 7th book, so I'll add a spoiler warning here...
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The trio wearing that locket which keeps getting heavier and manipulating them and making them feel worse and downtrodden so they have to take turns. And then it talks to Ron and tries to get him not to destroy it. I was really glad they finally got rid of that thing because it was obnoxiously like Frodo carrying the ring.
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I've found a lot of books that have a lot in common with the Harry Potter series. LotR is the really big one though.