In the first season finale of HSDK, when Kenichi manages to turn the tide of the fight by consecutively channeling the personalities of his five masters. Awesome and hilarious.
Also, one moment that really stayed with me in "Detective Conan" was at the end of Shinichi's first meeting with Heiji. After Heiji's spent the entire episode trying to prove himself the superior detective, Shinichi enters in grown-up form, with total class, and proves that Heiji's deductions were incorrect as he catches the real culprit. Heiji, suitably impressed, is honest enough to concede defeat to his rival's superior investigation skills...
...only for Shinichi to say that winning or losing in this context is meaningless - "in the end, all that matters is the truth".
Shinichi, Y U so classy?