After experiencing a lot of trouble with the onboard Broadcom BCM5721 Gigabit Ethernet interface of my new server I decided to get a network card that would be suitable to replace it. As Intel PRO/1000 MT PCI cards worked very well for me in the past I bought an Intel PRO/1000 PT PCI Express card.
The Intel PRO/1000 PT is supported by NetBSD 4.0 and newer and works like a charm for me. According to TTCP its Intel i82572EI chip provides a 13% higher transmit rate than the Broadcom chip. It also supports hardware-assisted checksums and TCP segmentation for both IPv4 and IPv6. Above all the card performed flawlessly in my server for over a week now with all the hardware features enabled.
So if you are looking for a fast and reliable Gigabit Ethernet PCI Express card the Intel PRO/1000 PT is a good option.