Pluto is amazing. If you can read the original (localized as Astro Boy Vol. 3), it's that much better. You suddenly get the feeling that the Tezuka original was the story from a child -- Atom's -- point of view, and Urasawa's version is the story from a real-world view. It's like Watchmen for 1960's manga.
I haven't read 20th Century Boys yet, but I'm getting to it soon.