Cisco VIRL is a great tool but it is artificially limited to a maximum of 15 nodes today. I have created a petition to collect names to send to Cisco, to show that the community really wants to increase this
Greg at Etherealmind has a call for educational IOS up on his site. It had to be redone because the signatures were lost from the first round. Dynamips is great but it has it’s issues and takes a lot of horsepower.
As many of you know, with IOS 15.0 Cisco has moved to one IOS per platform with different licenses for different features. This certainly means fewer versions to administer but it also means that the future for Dynamips/GNS3 isn’t looking