I need some more recommendations for manga. Any suggestions?

Here's what I'm reading/have read:

Current Series:

1.) Metal Heart (Otaku Boy Plays Ultimate, Real Life Dating Game For The Fate Of The World.)

2.) Nagasarete Airantou (Boy On An All Girl Island)

3.) Orihime Vs

4.) Rosario+Vampire

5.) Umi No Misaki (Recommended)

6.) Megaman Nt Warrior (Just Need To Read Volume #13!!!)

7.) Pastel (Normal Boy Meets Girl Senarios)

8.) Princess Lucia (Female Angels Vs. Demon Girl Trying To Prevent The Conception Of A Monster Born From A Human)

9.) Get Backers (I Prefer The Anime Over The Manga Partly Because It's Less Gorey)

10.) Super-Dreadnought Girl 4946 (Giant Girl Fighting Monsters)

11.) Addicted To Curry (Great Series Thus Far!!!)

12.) Hakoiri Devil Princess

13.) Asu No Yoichi (Samurai In A Modern World Romance)

14.) Mayoi Neko Overrun! (Catgirl Series)

15.) Kimi No Iru Machi (Romance)

16.) Pokémon Adventures (Manga)

17.) History's Strongest Disciple Kenichi Manga (Sequel/Spinoff To Tatakae! Ryouzanpaku Shijou Saikyou No Deshi)

18.) Zetman (Really Dark. Not Recommended For The Feint Of Heart.)

19.) The Legend Of Zelda: The Phantom Hourglass

20.) Unbalance X Unbalance

21.) Cyborg 9

Completed Series

1.) I''s

2.) D.N.A^2

3.) Video Girl Ai

4.) The All New Tenchi Muyo!

5.) Dragonball Z

6.) Lilim Kiss

7.) Dears

8.) Mx0

9.) Ane Doki

10.) Tatakae! Ryouzanpaku Shijou Saikyou No Deshi

11.) Dragon Quest: The Adventure Of Dai

12.) Dr. Chanbelee (Oneshot)

13.) Woman In The Man (It's A Temporary Bodyswap Manga) (Oneshot)

14.) Nisekoi (Oneshot)

15.) Dog Style [By: Minamoto Yuu] (Oneshot)

16.) Mär Omega

17.)L∞P Manga (Oneshot)

18.) Akazukin Eliza (Oneshot)

19.)Mär, A.K.A Märchen Awakens Romance

I may start One Piece because my one buddy is REALLY into it and although it's mainstream, I've been avoiding it only because I have a hard time getting into manga that doesn't have a serious tone.