1. 20th Century Boys (too bad volume 16 will be released only in April 30rd. Being scanslated by The Hawks
2. Berserk (volume 27 only in July)- licensed
3. Monster (released weekly by Mangascreener, just a volume and a half to end)
4. One Piece- licensed
5. Naruto- licensed
6. Pluto (new Naoki Urasawa project. Monthly manga, being scanslated by Mangascreener
)- this manga may reach a higher rank later. So far, only 6 chapters were released, so it's hard to tell if it'll be as good as Monster or 20th Century Boys.
7. Bleach- licensed
8. Yakitake!! Japan (being scanslated by Snoopycool
9. Black Cat (being scanslated by Chrono's Time Guardians
10. GANTZ (being scanslated by The Hawks
I'd really like to put Gunnm Last Order there too. However, there's no group scanslating it right now, and it's already licensed in the USA though.
Of course, these are the manga that are currently being released. My "true" top 10 is much different than that lol