Wow, can't believe I forgot this one. The one I'm currently rewatching is one of my favorites since I love detective stuff, evidence given by my awesome complete Sherlock Holmes book.
Detective Conan (Case Closed when translated to English) is an awesome detective manga and anime about a 17 year old super sleuth that when tailing someone looking suspicious at an amusement park, gets knocked out and poisoned. The poison causes him to revert to being the age of an elementary school kid, and is forced to keep his identity secret to prevent the organization that did this to him from finishing the job. He ends up living with his best friend (love interest) since his parents are away. It's full of suspense, drama, and loads and loads of humor. The situations create a lot of funny moments, and I just love it. Started watching when I was a kid, but when it stopped airing on tv, I forgot about it for a while. When I came to college, with nostalgia setting in, I remembered it and have watched through about 100 of the episodes. It's still ongoing, though the creator says he knows how he's gonna end it.