Code Geass, both Seasons can be considered a nice anime, the first season beating hands down the second.
The story of a fallen prince to an empire who with incredible wits and a power to have someone to obey him no matter what, tries to have the empire fall and take over the world.
Mechs, strategies, battle for power, C.C.....

Death Note before the time skip (to prevent from spoilers I won't say more)
A genius on earth stumbles upon a particular note book. If he writes a name in it with the image of the person in mind, said person dies. If details for way of dying are written, the scenario will play provided it's possible for the person to follow it.
A story about a guy who thought he was so good, wanted a better world and ends up... well you'll see.

Macross Frontier
Typical love triangle caught in a Space Opera. Worth watching for the many eyegams you may experience. It's useless to watch it with over compressed video files. Seek for HD files only (true ones)

Kamichu!
Tells the story of a young school teen girl who is a God. Nice and peaceful slice of life show, with a very nice feel to it.

Paradise Kiss
Tells the story of a teen girl entering the fashion world as a model for a young team of creators. Nice OST with nice images, overall nice to watch.

OAV: 5 centimeters per second
It's an animated movie, not a series. But it's worth watching.
I won't spoil it too much, it's about how life separates people eventhough they have feelings (but any description lacks a lot compared to the actual show you have to watch)

There are numerous other shows, but without any specifics the risk is to give to many answers that do not fit preferences. Eventhough at times, you can be caught from the left by a show you thought you'd never be interrested in...