Rurouni Kenshin - samurai stuff, really great. The Manga is better than the Anime in my opinion.
King of Bandit Jing- I was obsessed. Its' about a kid who can steal anything! Truly amazing art style, and the anime is on par with the manga.
Trigun- Great for those of you who like gun-slingers with a little comedy and sci-fi
Evangelion- only read mangas 1-2 but it was great.
Android Kikaider- I loved this personally. I saw somebody else mention it too so I thought I would. The animated series is genius. I loved how you really got to know the carachters.
.Hack//Sign- If you loved the game, you'll love this. I personally hated the games, but this series was amazing. Too bad every time it got to the end, Cartoon Network would start it over.... jerks....
InuYasha- This show is great. I love the music. I havent read the manga, but I'd like to. Catch it on Cartoon Network on saturdays to see the newest episodes.

On that note of demons-

Devil May Cry- they're making a manga of this one. It will be released on october 11th I think. I haven't read it *duh* but I have a lot of hope for it. Dante has always been a favorite of mine, and I hope the manga lives up to the potential. I'm defenately gonna buy this one. See more here- http://www.tokyopop.com/devilmaycry/