Here's a nice thing - LinuxStamp!
An open-source design, but you can buy one ready-built for only US $120 anyway.
* Atmel AT91RM9200 processor (Arm9 processor with MMU, 180Mhz operation)
* 32MB SDRAM (Only limited by 1x 54-TSOP SDRAM chip)
* 8MB SPI Dataflash
* 1x 10/100 Ethernet
* 1x USB host port (allows wifi adapters, flash drives and other USB devices to be used)
* 1x SD card slot
* Serial debug port access through FTDI USB/Serial converter
* JTAG port
* 2-Layer PCB design
* POE capable (48v -> 5v Power supply can be implemented on a motherboard)
I'll definitely be considering this for my future projects.
Mind you, Hammer and Nails is good too.