There is an interesting usage of the Cisco ACE to balance output internet traffic through different ISPs, as explained here.
Basically, it would be set on ACE the ISPs border routers as the rservers, a server farm in transparent mode (no NAT in the destination addresses), SNAT pool in each ISP VLAN and a VIP that would be used as the default gateway on your network.
Has anyone implemented this? In other words, has anyone used an ACE to load balance a pair of routers?
Note: A router running BGP would be a better solution, but it is not always an option.