There are a number of amp simulation plugins and cabinet emulators available online. Some are pretty pricey and some are free.
One of the more popular free plugins (with the option to donate) can be found on the LePou Plugins blog.
There’s an amp pack to download that comes with 5 separate amp sims and there’s a cabinet emulator called LeCab 2 as well.
The download links are located on the sidebar partway down the page. The plugins are available for both Mac and Windows.
The LePou Plugins blog features some examples if you want to hear how the amp sims sound, including some new high gain amp sims that are under development. The video below demonstrates several of the amp sounds and settings as well.
LePou Amp Sims
There are five amp sims included in the LePou plugins package:
LeCto – Was inspired by a popular high gain head (the Mesa Boogie Dual Rectifier) and includes 2 channels with 3 modes each, and a variety of controls.
LeGion – A high gain preamp sim that is an original piece of gear not based on real hardware. It features 2 channels with 2 modes each, 2 assignable tonestack, and drive and tone controls.
LeXTAC – A bit of a throwback based on a popular Californian boutique amplifier. It has 3 channels, each with 3 Pre EQ settings.
Le456 – A preamp sim with a design based on an ENGL Powerball Amp. It has 2 channels with 2 modes and tonestacks per channel.
HyBrit – A sim pack that sounds like Marshall amps.
LeCab 2 Cabinet Emulator
Amp sims aren’t much good without a cabinet emulator to load in your favorite Impulse Responses to get the best tone.
LeCab doesn’t come with any Impulse Responses preloaded, but there are a number of places to download some online, both free and paid.
LeCab 2 lets you run up to 6 simultaneous impulses, there are a variety of filters and effects, including phase and delay, and latency control down to 64 samples.
Update: Unfortunately LeCab is only available in 32-bit for Windows. If that’s a problem you can use this other free IR loader called NadIR, which has a 64-bit option.