It's hard to make a recommendation without knowing your tastes or what you want to see more of. Personally, my tastes change depending upon my mood.
When I feel like action: Black Lagoon, Hellsing, Sword of the Stranger, Ninja Scroll
When I feel like comedy: Ranma, Strawberry Marshmallow, Karin, Kimagure Orange Road, Lupin III
When I feel like romance: Maison Ikkoku (but you have to have a TON of time), Fushigi Yugi
When I feel like a heart-warming show salfe for kids: Cardcaptor Sakura, Someday's Dreamer.
When I feel like fantasy: Record of Lodoss Wars, 3x3 Eyes, Escaflowne, Bastard!!
When I feel like a good mix: Samurai Champloo, Cowboy Bebop
Martial Arts: Fighting Spirit (be careful, addicting!)
Yeah, I'm old so my choices reflect that a bit. However, I prefer to think of them as classics! :animesmil
I've seen the first part of Witch Hunter Robin and it seems fun, but my friend at Bandai who worked on the show cautioned me that it didn't end well, so I've been afraid to ruin my good opinion by finishing it. Dragon Ball can be a lot of fun, but there's a ton of forgettable episodes. Heck, all of these recommendations are good, although I have trouble committing to long series.
Here's a couple of short ones: 3x3 Eyes, Armitage III (go for the OVA if you like hard sci-fi, otherwise see the dubbed movie Polymatrix), Bastard!!
Can anyone recommend some good series with 3 DVDs or less? (not feature films, I've already got a fat list of those).