Thanks Andrew.

But as I understand both of these approaches are for backup external links for e.g. if one fails the higher cost link or the monitored link takes over.

I have two external trunked VLANs coming into my ASA on the outside interface (divided into sub-interfaces), is there anyway to make the traffic originating on those VLAN's go through separate routes?

Thanks.

You should check this

http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_configuration_example09186a00806e880b.shtml

The ASA doesn't support policy-based routing or load balancing out different interfaces. You can load balance to multiple next hops if they are out the same physical interface (i.e., two internet routers plugged into the same switch as the ASA).

Unfortunately the only thing you can really do is route tracking or ip sla as described by the other users.