do you think the LPC812 is as good as any
Probably, although it's note available yet. Although as was pointed out above the LPCXpresso board is and to start with that's all that matters. The LPCXpress system is very good.
or is there a model you'd suggest?
Well I'm pretty much into the LPC1227, at 48 or 64 pins and with 2 UARTs I find it's about right for what I'm doing now. I liken it to the Mega1284 which I think is the best AVR around. I like those chips so much my current PCB has one of each 
I've written a lot of code for the 1227, originally just to learn the chip but it's slowly turning into a proper Arduino-style HAL. See here
http://lard.robgray.com/index.php
I've spent the last couple of days getting the serial Tx working, it's all FIFOs and interrupts and an unfamiliar chip but it's going now. See here (my 3-day old blog) for today's trials
So, at the risk of being biased I'd recommend the 1227, but one thing I like about the LPC range is that they go from 8 to 217 pins so there's something for every one.
Rob