My favorite is LSD and DMT. 

Nick Sand wrote about vaping DMT at the tenth hour of a LSD trip and I have tried that.  I preferred vaping at peak.

There is a really nice synergy between LSD and DMT! I felt like the transition into the DMT realm was much easier than sober. I always had a great experience with the combo. I always enjoy LSD and so I am always in a good mood when I take it, this translates to good experience into the DMT.

What always strikes me odd is that the DMT kind of overides the LSD.  Meaning that when I vaped the DMT I was no longer feeling the LSD. I had expected to have the feeling of tripping LSD in DMT hyperspace.  Nope.  It would transition from LSD tripping, to DMT hyperspace, and back to LSD tripping. As I mentioned, the transition is practically seemless and gentle.

I feel like your mind is already halfway primed for the DMT journey when your on acid. It is ready to go and I always felt relaxed before.  The first time I did this combo I had a hard time trying not to laugh before I bagan vaping the DMT.  I was already giddy!  Next to no apprehension at that point. Just went for it.  I have done this combo three times. At peak twice and at tenth hour once after reading that Nick Sand blog.