I only discovered anime in January, so I'd better not try and nominate a BEST EVER, but would like to list in order of loveliness those of which I've watched more than a couple of episodes so far:

1. Ichigo Mashimaro, all 12 eps x 6 times
2. Card Captor Sakura, both series and both movies
3. Kodomo no Jikan, OVA + 7 eps (+ 32 manga) so far
4. Pita Ten, all 26 eps (+ 50% manga)
5. Lucky Star, 8 eps so far
6. Pani Poni Dash, 6 eps so far
7. Hidemari Sketch, all 12 eps x 2 times
8. Moetan, 5 eps, including 2 without subs so I had to read the 'body language'
9. Chobits, all however many eps
10. Tokyo Mew Mew, all 52 eps
11. PGSM, 24 eps so far
12. Sailor Moon, 22 eps so far
13. Kanon 2006, 13 eps so far

I think I would probably like Kanon more if I managed to focus more on the plot and less on the loli when watching anime, but I always think Ichigo will be top of my list