here is a great article for configuring small site multi-homing without using BGP: http://www.nil.si/ipcorner/RedundantMultiHoming/
You can get multiple T1s. The cost is high, but you can bond up to 8 T1s together for a total of 12 megabits. You lose a little bit of latency in the MLPPP protocol, but you would still be looking at less than cable. But, yes, a congested T1 would have high latency, just like any other congested transport medium.
That said, if you're happy with the performance and stability of your cable and DSL connections, there's little reason to spend the money on bonded T1s. IP SLA will get you the failover you need and can be tuned to be very quick.
indeed...if your budget can fit it try a 2901. the ISR G2's have about 3x the throughput of the old ISR's and should cost about the same (new). the 29xx should give you a good bit of growth. to be honest i just hate how the 1941's look ;PAny Cisco device should do it. While I haven't had a chance to use them yet, I'd imagine that the Cisco 1941 would fit the bill. Or you could look at getting a used 1841. I wouldn't really venture too much lower than that. Either way, you'll also want to pick up a WIC-1ADSL or HWIC-1ADSL to go with it. Doing that is better than relying on an external ADSL modem, in my opinion.