I would say Bleach, but that is too current. Maybe in a couple of years I can gauge its greatness accurately.
Right now, my favorite all-time anime would have to be:
[x] Gundam Wing
[x] the entire Ghost In The Shell canon
[x] Hellsing [both OAVs and TV versions]
[x] Sailor Moon
[x] Last Exile
And if I met a n00b to anime, I'd probably rec them to that person.