Good Thunderbolt network cards for Mac?
If you'd like to add wired network (Ethernet) ports to your MacBook Air you have the following options:


A single or dual Thunderbolt network adapter. Apple makes one, the MD463ZM, but only with a single network port. There are third party adapters that provided more than one port - for example the Sonnet Twin 10G. There are also Thunderbolt docks that contain single Ethernet ports (for example from Sonnet, Belkin, CalDigit, etc).
One or more USB ethernet adapters.


Note - as the MacBook Air only has a single Thunderbolt port, if you use that port for an Ethernet adapter you cannot use an external display at the same time. One way to work around that is by using one of the Thunderbolt docks described above.

The most cost effective route is probably to get a single port Thunderbolt adapter and a USB 3.0 Ethernet adapter. If you'd like to use an external display at the same time as the two Ethernet ports, get a Thunderbolt dock instead of a Thunderbolt Ethernet adapter.