Oh man, that is tough... there are a number that I really like.
In no particular order, just when they pop up.
1. Bishoujou Senshi Sailor Moon (S and Stars are my favorite seasons. Saturn, FTW)
2. Mobile Suit Gundam: 8th MS Team (Really well done, IMO. Best character development in Gundam, plus my favorite gundam fight in episode 10)
3. Tengen Toppa Gurren Lagann (We can do whatever though the sheer power of our AWESOMENESS!!! FEAR IT!!)
4. Cowboy Bebop (Need I explain?)
5. Suzumiya Haruhi no Yuutsu (Again, need I explain?)
6. Kodomo no Omocha (hilarious. What happens when a Shoujou series is on CRACK)
7. Death Note (Another, no explaination needed)
8. Black Lagoon (Most violently hilarious series I have ever seen)
Other good series, or just certain parts that I like:
1. Tsubasa Reservior Chronicle (the OVAs Tokyo Revelations and Shunraiki. Not a fan of the anime, but the manga is fun/entertaining/CLAMP, WTF IS GOING ON?!)
2. xxxHolic (See above statement for manga... and it is actually LESS confusing)
3. Code Geass: Hangyaku no Lelouch (Very well done, but... it gets... really over the top later...)
4. Bleach (it's fun... that's all I can really say, up though Soul Society arc was great... after that, it kind of... got way, way, way overboard)
5. Chobits (Manga, not anime. Anime is... well, mainly filler, and it's not as well done as the manga)
6. Kodomo no Jikan (Psychoanalysis, FTW! Freud, you magnificant ******* you... so many psychological issues in this it's astounding)
7. Rurouni Kenshin (The matrix with swords)
8. Cardcaptor Sakura (Again, just something fun. Manga's better though... and yes, I do like CLAMP's stuff)