I prefer "found object" bookmarks over the intentionally designed kind, like if I get a book at a brick-and-mortar store, I usually end up using the receipt as my bookmark. Here are a couple of my favorite bookmarks right now.
My extremely cool in-laws slipped this little note into the birthday card they gave me:
Like most rectangular slips of paper I've requisitioned for these purposes, I fold it in half down the longer axis when in use.
Here's the bookmark I've been using lately for larger books:
That looks like several playing cards, but it's actually a packaging element for a fancy-pants electro-gizmodic edition of Uno. I don't think it's any better than the regular version of the game, but the string of fake cards on the box is kinda cool.