For commercial projects, the MAX3421E is supported by USB Stacks from HCC-Embedded and Micro Digital. HCC-Embedded also has an SD card module to add a USB Host to any board with an SPI capable SD card socket. The schematics and layout are a free download from the website.
The MAX3421EVKIT-1 from Maxim can also be used for developing a USB stack for individual devices. It can be ordered directly from Maxim ($57) or from Digikey ($62). You can start with the MAX3421E EVKIT-1 Software and User Guide to develop your own driver for targeted devices. I have been working with the MAX3421E with an ARM processor board and have added support for a mouse, keyboard, and hub to the design.