all these animes i'll be naming will contain romance as the main plot, some will be lighthearted, others will be dark but all these anime i've ENJOYED but yet to see on your (entire/full) list so hope you check them out! All of these are good+ in my opinion
Acchi Kocchi (a lighthearted comedy anime that you shouldn't miss)
Amagami SS (concept is similar to TWGOK)
Bungaku Shoujo: Memoire (the OVAs, watch them if you loved the movie)
Da Capo (it has a bunch of seasons, but it's pretty similar to Kanon, yet different)
Futakoi (twins
)
Kimi no Iru Machi (Short OVA series, but nicely adapted from it's popular ongoing romance manga)
Kimikiss Pure Rouge
Koi to Senkyo to Chocolate (all is good if you ignore that exaggerated censor)
Kowarekake no Orgel (not actually romance, but is another form of love.. the story is beautiful)
Mai-HiME (Amazing anime, nothing else to say.)
Mayo Chiki!
Myself ; Yourself (alot of drama but great)
Nagareboshi Lens (short OVAs, again it's something you can't forget after watching)
Omamori Himari
Shuffle!
though I don't know about recommending these, just thought I'd share these titles anyway for you can check them out if you want more to add.. Some of these titles don't have romance as the main plot but isn't ignored:
Fortune Arterial
Gift: Eternal Rainbow
Haiyore! Nyaruko-san (heroine might be too deredere for you)
Maken-Ki! (might be too ecchi for you)
Saikano
action/romance?:
Dragon Crisis!
Dog Days
IS: Infinite Stratos
Dragonaut: The Resonance
Tayutama: Kiss on my Deity