Question : Two Internet connections to same internal network

I have a customer that has an existing T1 to the Internet which has servers behind a firewall with static NATs if needed.  Standard stuff.  They now have brought up a second Internet connection and would like to be able to access their machines over that as well.  They want to be able to do this without touching anything on their servers if possible.  So those external IP's will be different of course and on a different internal subnet.  Whats the easiest way to grant access to the servers over either pipe.  Some of my ideas were

Two NIC's in each server with one on the old internal subnet and one on the new.  This seems to be the easiest solution but involves taking servers down in some cases.

placing another router in between the servers and the new subnet and NATing the the new internal ips to the old internal ips.  Double natting makes me nervous.

Any other ideas I'm not thinking of?

Answer : Two Internet connections to same internal network

Issues here are:
1. You cannot NAT two different public IP's to the same internal IP - at least not with your typical firewall. Q: What kind of firewall do you currently have?
2. Most firewalls only allow one default route out. Which ISP are you going to point to and how do you handle load/failover?
3. Windows servers can only have 1 default gateway so that negates ged325's suggestion. Which firewall in the diagram is the default?

There are several Dual-WAN firewalls out there. Linksys, Sonicwall, Fortinet, Zywall, Xincom, Radware pick one. . .
Cisco does not have a product like any of these.

Bigger companies might use something like a FatPipes appliance
http://www.fatpipeinc.com/superstream/index.html

Rid,
> pointed to one machine, the responses would go back to the router/gateway from which the request came....
Nope. The machine only knows the destination IP and one path out - through the default gateway.
That gateway has a route to the destination. The router can only look at the destination and send it to the next hop gateway, most likely its default.