Router Solution For Any Business Needing A Reliable Cost Effective High Bandwidth Internet Connection (e.g. DS3 Bandwidth)
The simplest solution is indeed a spe############t off the shelf router which handles dual WAN and understands failover with failback and load balancing etc. However there's a problem with most kit currently available in the SoHo market; they're not especially robust and resilient and they often don't have good tech support.
By contrast enterprise market solutions from the likes of Cisco aren't cheap and require a level of Cisco awareness that can take months or years to acquire.
There's another and more complex issue to consider when you have 2 WANs from diverse suppliers; session failure. Packets for a specific session - such as a connection to a web browser - generally travel on only one of the 2 WANs - in other words you make a connection to your bank via only one WAN link and the return packets from your bank come in on the same link. If that WAN fails or becomes unreliable during the session the packets won't magically start travelling down the 2nd WAN. You've lost your session and you have to start again. For some environments this isn't too critical; for others it can be life threatening. Only you can judge the risks.
However if you have 2 WANs from the _same_ supplier then it may be possible to arrange for bonding and failover/failback to take place at their end of the link; in those circumstances the packets _WILL_ continue to flow even if one WAN fails. Some suppliers here in Europe will even supply managed routers to maintain the services for you; can't speak to the US market but I'd be surprised if similar services were not on offer..
If you decide to go with a diverse supply using 2 or more WANs then the simpler alternative to buying a spe############t dual WAN router is to roll your own solution using an older PC [such as a P3 of circa 1ghz with 512mb ram and a small disk] with multiple network interfaces and one or other of Smoothwall or pfSense - which are open source distributions of spe############t firewalls designed to do exactly what you describe: deliver failover/failback and load balancing etc.
Installation of pfSense in particular is relatively pain free and can be up and running in about 90 minutes or so if one takes the trouble to read the docs carefully [shock horror: an IT professional should RTFM?].
For help navigating the maze of issues to find the most cost effective solution …. and comparing what is available from multiple vendors (e.g. T1 Bandwidth, DS3 Bandwidth) … I recommend the free services found at Bandwidth Solution
. Their help includes a low price guarantee from the providers they list.