Steve Fryatt is a well-known face in the RISC OS world and a regular fixture at RISC OS shows where his stand always has lots of interesting software.
His website hosts lots of free software including the free home accounts software CashBook. This has recently reached release 1.41
There are utilities like Locate, PrintPDF and PS2Paper, lots of games.
If you are looking to write your own software, there are Build Tools and a guide to Wimp Programming In C
Steve also has some interesting pages on his website on his non-RISC OS activities.
Steve Fryatt's website