It depends what you like as to what I'd recommend. There's tons of good series of just about every genre. Also, have you seen many series? I'm not sure whether I should recommend well known series.
I don't really have a single favourite series, but I would recommend watching as many different types of series as you can to get a good feel for things.
Here are some good series, all of different genres:
Chobits
Black Lagoon
Samurai Champloo
Macademi Wasshoi
Cross Game (Currently airing)
Code Geass
Higurashi no naku koro ni (many people don't like it, but many do like it too)
If you have (or find) a series you like, I can also recommend similar series. Hopefully, you'll find something you like.
Only admins/staff/mods can post anime on the main page if that's what you mean.