My list:
Love Hina
Kami no Mizo Shiru Sekai (The World God Only Knows)
Detective Conan (Case Closed)
Hayate no Gotoku (Hayate the Combat Butler)
Mahoraba
Midori no Hibi (Midori Days)
Naruto
Kashimashi (Girl Meets Girl, it's shoujo ai, but the story is pretty good, if you can handle the genre)
Mx0
Kannagi
Suzuka
Karin (Chibi/Cheeky Vampire)
Kimi no Iru Machi (The Town Where You Live)
Nogizaka Haruka no Himitsu
Nagasarete Airantou
Mahou Sensei Negima! (Magister Negi Magi, not to be confused with Negima!
? and/or Negima!
Neo)
Ef - A Fairy Tale of the Two (to be frank, one fuckin' confusing story, it's good if you can explore its deep meaning, only if...)
Clannad
Room no. 1301
Kanon - Honto no Omoi wa Egao no Mukougawa ni, there! I've typed it (another confusing shit but good overall. For those who hates innocent harem logic, don't read this one, note that this one contains no 15+ material). Other names: Kanon ~each regret of Kanon~ or Kanon: The Real Feelings of the Other Side of the Smiling Face, fuckin' title. Not to be confused with Kanon by Morishima Petit, same settings, slightly different story
Fortune Arterial
Edit: forgot one: Law of Ueki
What else.... um... my other lists are 16+, 20+ in some cases, so that's all there is to it
Also, take note that while some might have English names, those are translations of the Japanese title. Might help in searching for it, but some never made it to being licensed in US. A good example is Kami no Mizo Shiru Sekai, which english name was provided by the author himself, not by english licensor