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Getting the right hardware is essentially a matter of checking that what is supported in your system meets the needs of your network. It's always good practice to check the hardware compatibility lists at your operating system's website. You could also check the man pages or use apropos keyword commands (where keyword is the type of device you are looking for). Searching the archives of relevant mailing lists is also useful if you feel you need more background information.
You should be aware, though, that some hardware comes with odd restrictions. One such example is hardware that depends on firmware that is loaded onto the card. Often in these situations, the manufacturer refuses to grant redistribution rights for the firmware, and operating systems such as OpenBSD can't package it with their releases.