Here are some helpful links worth knowing:
Key Rollover Test
Try the Key Rollover Test if you want to find out which key combinations work on your keyboard or you want to know how many inputs your keyboard can handle at once.
The Deskthority Wiki is probably the most comprehensive wiki for keyboards and other input devices. There are tons of useful articles as well as extensive lists of available mechanical keyboards and switches. Some of the articles on Mechanical-Keyboard.org use resources from this wiki. Thanks a lot for sharing them!
The Geekhack Forum is one of the best addresses if you want to discuss about keyboards. The community consists of almost 50.000 members.