The K107 looks good but it has a awful number of limitations.
Just to clarify some things sort of mis-stated above. Peter Anderson http://www.phanderson.com created the LCD1x7 and LCD1x8 series of PIC chips (currently 16F648A) that serve as the core of the serial to parallel conversion for a HD44780 character based LCD display. He sells the chip and packages a schematic with it.
The K107 is a pcb I designed to house Peter's chip. It s a flexible design which can accomodate 2x7, 1x10, 1x14, and 1x16 pin configurations (2x8 has been added to Rev 4 of the board which will go to production runs in the next month or so). Peter's firmware allows handling of 2x16, 2x20, 2x24, 2x40, 4x16 and 4x20 character geometries (software selectable). The signal input can be TTL TRUe or RS232 INVerted (jumper selectable) and can be had in 2400 baud, 9600 baud, or 19200 baud. The serial baudrate is fixed in firmware specifically to avoid the potential problems, some of which have been discussed above. The K107 board with an Anderson chip comes up running every time. The Anderson firmware provides for all the expected LCD controls, as well as customizable characters, customizable startup splash screen, 4 line high numerals for large displays, etc.
The Anderson chip uses the PIC internal UART and has a 64 character buffer so a very busy display may require some 1-40 ms delays. LCD displays are not fast devices these delays are going to happen no matter how fast you get data to the control board, whether it be serial, SPI or I2C
I wrote a complete library for the K107 based upon the TX part of Software Serial. I run my displays at 19200 on my Arduino and BBB boards all the time with no problems.
I would be interested to know exactly what you feel are the 'awful number of limitations'
The K107 Serial LCD Controller can be seen at http://www.wulfden.org/k107/ and my Freeduino offerings (incuding some bundles with K107 boards and displays) can be seen at http://www.wulfden.org/freeduino/freeduino.shtml.
By the way, while the original Anderson design called for a TIP41C (TO220) to PWM the display backlight. That was overkill. I found that a 2N4401 (TO92) in the negative line of the LED backlight was more than adequate for even the brightest 4x20 backlit displays. I have sold nearly 2000 K107 boards and not one user has complained of the 4401 burning up or getting hot.
cheers ... BBR