Mine

# The loopback network interface
auto lo
iface lo inet loopback

# To box0
allow-hotplug eth0
iface eth0 inet static
        address 192.168.1.1
        netmask 255.255.255.0
        network 192.168.1.0
        broadcast 192.168.1.255

# To another subnet
allow-hotplug eth1
iface eth1 inet static
        address 192.168.2.1
        netmask 255.255.255.0
        network 192.168.2.0
        broadcast 192.168.2.255

# To neighboor
auto ath0
iface ath0 inet dhcp
        wireless-essid Wireless
        wireless-mode Managed
        wireless-channel 3
        wireless-ap 00:11:6B:10:A2:0A
        post-up iptables -t nat -A POSTROUTING -o ath0 -j MASQUERADE
        post-up echo 1 > /proc/sys/net/ipv4/ip_forward
        pre-down iptables -t nat -D POSTROUTING -o ath0 -j MASQUERADE
        pre-down echo 0 > /proc/sys/net/ipv4/ip_forward