I've seen tantei gakuen Q a LONG time ago, in some shitty animax clone local channel a couple of years ago.
EDIT: not that animax isn't shitty, but this channel was even shittier since they censored the series A LOT
You obviously haven't seen Meitantei Conan
Detective shows are awesome . I've only watched the dubbed Case Closed, after 130 episodes and 6 movies that were dubbed it would be really weird to watch it in Japanese. Speaking of detective shows, I've seen CC, Spiral, and Mythical Detective Loki Ragnarok, any good ones I'm missing out on? No subbed suggestions please .
To be honest, I was avoiding watching subbed stuff for a long time as well, but then I finally decided to go for it with High School of the Dead, and it opened up so many doors. And filled up my hard drive. :'(
If you hadn't said no subbed, I'd totally say TANTEI OPERA MILKY HOLMES. It has "tantei" and "Holmes" in the title. Clearly, it shall be a fantastic detective series. But it's also about little girls, so maybe not.
There are a lot of series where the English dub is better than the Japanese. And dubs have been getting progressively better since the 90s. Aside from porn, almost everything dubbed in the past 5 years has been really high quality.
It's up to personal taste as far as I'm concerned. I've heard Black Lagoon's dub which is apparently holyshitawesome, and yeah, it's not bad. But I wasn't especially blown away. Plus, once I associate a character with a specific JP voice actor, for me it's hard to switch over.
Also, did someone say detectives? If so, obligatory Death Note mention.