If you enjoy Aliens, Time Travellers and Espers, then watch The Melancholy of Haruhi Suzumiya (14 Episodes). Possibly one of the greatest anime's I've seen so far.
Also, if your looking for something quick which includes robots and such, FLCL (6 Episodes) is really good as well.
BUT, if your into all that perverted stuff, Golden Boy (6 Episodes) is for you.
For 5cmspersec, you said that you liked romance. If you haven't already, I would watch NANA (39 Episodes?)
A Simple Girl
Living In A Complex World