Hi,
I stumbled across a really interesting update to Waves Studio Rack that released earlier this month. Studio Rack is a plugin host, that can be used within any DAW. Before the recent release Studio Rack could only host Waves plugins, so was useless if you did not have Waves plugins.
The recent release adds support for VST3 plugins, and works like a charm in Acid. Best of all, it's free.
This is particularly useful because the plugin itself appears within Acid as a VST2 or VST3 plugin. Although I personally have experienced no problems using this plugin in its VST3 form, others might. Using the VST2 version allows you to operate VST3 plugins in Acid with better compatibility - as an example of that, I have an issue with Kilohearts plugins and automation, but using Waves Studio Rack I no longer see that particular issue.
Prior to this you would have to resort to something like DDMF MetaPlugin, or SuperPlugin - neither of which are free.
Studio Rack does not support VSTI plugins, so you can still resort to DDMF's solutions for that. SuperPlugin is a super easy way to get things like Reason working within Acid.
Better plugin compatibility would be better, obviously. Until then, there's VST hosts!