aCard + Tri-Band for Mac Mini
802.11 a/b/g/n for Intel Mac Minis
*will not work for PowerPC Mac Minis, please check before ordering. Works for older Minis not the new ones that came out in August 2009

Not even Apple offers this.
This is the best wireless conceivable for Mac Minis. This goes beyond an 802.11 n upgrade. This new product allows for full wireless speed. The QuickerTek aCard provides 802.11 a, 802.11 b, 802.11 g,
and 802.11 n wireless compatibility. What that means is the computer can network using 802.11 a and the 5 gigahertz band. What this means for you: a cleaner signal with far less dropout. The 2.4 ghz band is crowded with other devices (including WiFi networks, cell phones, and microwave ovens).

Apple's new Base Station Extreme supports a/b/g/n but Apple won't upgrade your Mac to 802.11 a/b/g/n. Apple only offers 802.11 b/g/n in its Macs. This means they DO NOT support the 5 gigahertz band. The 5 ghz band is optional for 802.11 n, not mandatory.

This makes great use of MIMO technology. The 802.11 a/b/g/n devices aimed at high performance will include MIMO is Multi-Input Multi-Output, meaning both the Base Station (or Router) and the Mac (or PC) must have multiple antennas to employ something called “spatial-multiplexing”. This is most important in the speed department, think of it as having a 4 lane highway instead of a 2 lane highway, and having plenty of traffic for the former!

works with all the wireless standards*:
802.11 a - 5.0 ghz, 300 Mbits per second
802.11 b - 2.4 ghz, 11 Mbits per second
802.11 g - 2.4 ghz, 54 Mbits per second
802.11 n - 2.4 ghz, 300 Mbits per second

*actual speed dependent on AirPort Base Station (or Router) settings and physical barriers.