There is an interesting usage of the Cisco ACE to balance output internet traffic through different ISPs, as explained here https://supportforums.cisco.com/thread/2110390.
Basically, it would be set on ACE the ISPs border routers as the rservers, a serverfarm 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?
(A router running BGP would be a better solution, but it is not always an option)