fun,
Cisco use to host a couple but they are no longer available. Sites like internetworkexpert offer virtual labs but alas they are not free. GNS3 is free but requires an IOS and is not a virtualized/internet solution. It is an emulator. You may wish to check into some non-free software like Boson or PacketTracer. Now you did say for work as well which would mean that you probably have access to an IOS. That said, perhaps GNS3 is a possibility. Otherwise, visit internetworkexpert.com and buy some rack time.
Finally, a real lab is the best option. Check eBay and cablesandkits.com as well as Wendel Odoms articles, readily available from this forum, and hardware recommendations which is also prevalent throughout this forum. Sorry, but I have nothing free to offer that is web-based.
Billy Haines
CISSP Associate, CCNA Security, CCNA R&S, ETA FOI