So I was looking at buying a mechanical keyboard. Does anyone know a blue LED backlit one? Also I would like it to be sleek. None of those random shapes sticking out the side. An all black rectangular shape one with cherry mx blue switches would be preferred. Thanks.
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Do not buy the Corsair K90. It is not fully mechanical, and it does not even have Cherry MX Blue switches (it has Reds). Also, the 18 G-Keys are going to be completely useless unless you're doing MMOs (which you haven't specified). If you are, then the K95 is a better choice, as it is fully mechanical.
If you're just looking for an FPS keyboard, I recommend the Ducky Shine 2/3 (if you can get your hands on it), as they come with an insane amount of options as to backlight color, key-switch type, etc. If you don't need backlight, the Filco Majestouch 2 keyboards have spectacular build-quality and are great keyboards all-around.
Both of these keyboards fit your criteria (except the Filco one, in case you decide you don't need LEDs).
Also, on the lower end of the spectrum, Cooler Master makes some good CM Storm keyboards.