Click-N-Type virtual keyboard
You must read the disclaimer before downloading.
From the authors:
Click-N-Type is an on-screen keyboard which allows you to type with the use of a pointing device (e.g. mouse or tracker ball) rather than the physical computer keyboard. The designers claim it is successful in allowing text to be typed into “those uncooperative places like browser URL "Address:" fields, Email "To:" addresses, Email "Subject:" fields, and dialog boxes like "Open" and "Save As...",” which other virtual keyboards have trouble with. Several custom layouts are available, including QWERTY, ABC and ‘Speed layout’ in which the letters commonly used together are grouped together, reducing the pointer motion required. An English language prediction program is also available for use with the keyboard, available from the same website.
This is a flexible and powerful on-screen keyboard. To customise the keyboards you will need to be fairly computer literate, but other than that it is also quite easy to use. It includes basic word prediction.