 If you liked
Onegai☆Teacher
|
 ...then you might like
Golden Time
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They are both about how a certain disease influences the relationship between the two main characters. Also, the two main characters get together quickly in both of them, and there is one other girl who is in love with the protagonist that again, creates difficulties for the relationship of the protagonist.
Plus there is the smaller girl character who's the silent type and a bit mysterious.
Both the animes also have their healthy dose of drama involved.