In no particular order, some links I have found to be useful.
http://www.heyrick.co.uk/index.html Lots of useful guides
http://www.cp15.org/versioncontrol/ An SVN client
http://www.virtualacorn.co.uk/index2.htm MacOS keyboard tool
http://www.marutan.net/rpcemu/index.php An emulator
http://www.elesar.co.uk/ New hardware!
https://riscosopen.org/forum Discussion forum
http://www.riscosbits.co.uk/ Accessories...and of course Wispy!
http://www.cjemicros.co.uk/ Mostly old stuff, and Pi stuff
http://sdf.org/ An alternative OS!
http://glen.sdf.org/ One of my other sites...
http://www.mw-software.com/index.htmlTechWriter
http://www.netsurf-browser.org/ Web browser
http://www.rcomp.co.uk/ MessengerPro and other utilites
http://nettle.sourceforge.net/ SSH & Telnet client
http://www.cp15.org/webjames/ Web server
http://croftnuisk.co.uk/coltsoft/fireworkz Word processor
http://www.cp15.org/ RISC OS Software
http://www.apdl.org.uk/ DrawWorks and other useful stuff
https://forums.jaspp.org.uk/ Games!
http://www.sbellon.de/software.html Modules for printing
http://www.phlamethrower.co.uk/riscos/vnc_serv.php VNC Server
http://www.riscosports.co.uk Updated version of WebJames, Tesseract OCR program and others.
http://www.flypig.co.uk VNC Server and other tools
http://ftpc.iconbar.com FTP Client
http://rosery.net/riscos FTP Server
http://www.stronged.iconbar.com Front-end to FTPs and other stuff
http://riscossmbserver.sourceforge.net A Samba server for RISC OS (guide here).