I see that there are many Realtek RTL8169S gigabit cards going for a song on eBay.
I've always liked and used Realtek cards, and I use the RTL8169S in my servers. However, the RTL8169S has one problem: overheating. If you buy any, make sure they include a heatsink. Those without a heatsink are prone to locking up if the temperatures inside your case get too high.