pfSense-On-A-Stick - 802.1Q Trunking With pfSense 2.0 RC1 and Mikrotik RouterBoard RB250G Smart Gigabit Switch with five ports and SwOS v1.5 - Stefcho's Tech Blog
pfSense router-on-a-stick VLAN configuration with a Mikrotik SG260GS
MikroTik Routers and Wireless - Products: Woobm-USB