There is a new suite of open source (GPLv3) plugins on the block, Flo's Audio Plugins. The suite currently consists of 3 miked cabinet simulation plugins, based on various freely available impulse response collections. The plugins allow you to choose and blend various speakers, mics and mic positions and other plugin specific features such as a switchable mid-boost (linear filter Tube Screamer IR). Features for each plugin include -

Plugin for God's Cab IRs

combine two individually adjustable channels

various microphone models and positions

presence control

optional (linear) signal filtering with a Tube Screamer

extra room microphone section

Plugin for Kalthallen Cabs Free IRs

combine two individually adjustable channels

various microphone models and positions

two speaker types (V30, G12T75)

two power amp types (Tube, Transistor)

Plugin for GuitarHack's IRs

combine two individually adjustable channels

various microphone positions

There is also included documentation with the God's Cab and Kalthallen Cabs plugin downloads that go into detail about how the impulse responses were created. The God's Cab documentation in particular is very thorough and an interesting read. Included impulse responses for all plugins are available at 44.1kHz, 48kHz, 88.2kHz, 96kHz and 192kHz sample rates.

The plugins are currently in beta status and are available in either stand-alone form or as VST plugins, however, there is an LV2 version expected soon. Source code for the project is not currently hosted online but it can be requested from the plugin developer, Florian Bihler. Florian is currently looking into options for hosting the projects code. He is also willing to expand platform support, and the plugin range, subject to interest in the project.

Visit the projects website for full details and downloads.