Wow this is a great thread. I haven't quite finished it yet, but I can't wait to add my own input.
Cannabis + Everything: I have yet to find a drug that weed does not positively enhance. All of the following combinations benefited from the addition of cannabis.
LSA + Mushrooms This is one of those combinations that is greater than the sum of its parts. Body high and visuals were both amplified more than I expected, although I did experience a lot of "mind-fuck" towards the end of the trip.
2CB + LSD: Great synergy between these compounds, and overall a very clear-headed and "productive" trip. My dosages were low for both when I tried this combo, but I got the impressions that it would only get better as the dosages go up.
LSD + MDMA: I tried the infamous candyflip for the first time recently and it really is an epic combination. I had sooo much fun that night, but it isn't the most euphoric combo I have experienced, contrary to what I was told to expect.
Mushrooms + Ketamine /
LSD + Ketamine : I tried these combinations at a music festival this past summer and found them both to be awesome. Great body highs, cool visuals, and some of the best music enhancement I have experienced. I'm grouping these two together because I found them to be very similar; moreso than mushrooms and lsd on their own.
Mushrooms + DXM + Benzo: This was my first psychedelic combination, and still my favorite. Time your dosages right (Shrooms at T+1.5 is the key) and words will not be able to do justice to just how amazing this combination can be. Expect ego-loss, out of body experiences, and awesome CEVs bundled into fiveish hours of indescribable bliss. Here's my
retrospective on the combination.
DXM + Salvia: This combination is EXTREMELY dissociative. I had never experienced true "nothingness" before I tried this. Perhaps someone who really likes salvia would be able to appreciate this combination, but I found it to be way to disorienting and kind of uncomfortable.
Also: Piracetam enhances all 5-ht psychedelics (especially visually), but it is kills the effects of low dose dissociatives. I have heard that it has some cool synergy with dissociatives in large doses, but I can't comment on this personally.