not for free
There are many IOS images of different networks devices on the web, but some of them are the most used on GNS3, to do the networking exercises to practice or prepare CCNA, CCNA or even CCIE and real Labs of networking as if you were working with real network devices, since the images come with all the features supported, for example by a physical router or switch.
vitually impossible to get Cisco IOS without buying it from Cisco or Cisco distributors. Best bet is just buy a router with it.
It is possible
Look for a torrent or rapidshare file. I once saw a collection if ios on emule. One of my friend told that his assistant is downloading the collection from torrent
Cisco 1921 Router Ios Download
download cisco router IOS
What model is your cisco Router. i might be able to help you. The Cisco IOS not cheap. a whopping $315 just for a one year contract.
Price depends on Model
The price of the contract depends on the model. I have a small 871 at home and only pay $75/year for complete access to Cisco's documentation and software.
Technically, you should have a separate maintenance contract for every Cisco device you plan on upgrading, but I've never heard of them enforcing this.
download Freesco or Vyatta
http://www.freesco.org
http://www.vyatta.com/
Either one can run as a VMware appliance which makes is muuuuuuch easier to deploy.