A few weeks ago I posted a request asking for cheap (vs Olimex's MSP430 boards) EVBs with Ethernet to build a proof of concept and then use the design as the basis of a low-volume production run. I can't seem to find that thread, but here's a summary of what I decided:
Someone in that thread suggested Rabbit. It is a long time since I looked at Rabbit, but I took a look, talked to their sales rep, and wound up specifying the RCM3710 core module into my application. This is a SSL-capable 8-bit module, very small size, with 10bT Ethernet,256K flash and 128K RAM, 1M serial flash, and it's $32 in 1000 qty. A bit irksome that it is 3.3V, but the processor I/Os are at least 5V tolerant.
Presales support is good; I won't know how the ongoing support is until my customer says "yes" and I start building stuff.
Going this route saves me a lot of engineering time designing the Ethernet part and debugging a TCP/IP stack, plus it avoids the high cost of MACs in low quantities, plus the MAC address is provided with the core module.
The development system is moderately expensive ($700) but this is negligible (in other words, I'm not paying for it).