For one thing, names and titles for combos are pretty stupid IMO, because the experiences are very subjective on the individual and dosage. Dumber persons will go for combos they identify by the names, and might find themselves somewhere else, which is not always good.
Combos should be described by the names of the drugs involved.
The ones i tried so far:
Cannabis + LSD - Doesnt need description
Cannabis + Ketamine - I usually like to smoke a lot before injecting the K, which puts me in a much more vivid float. It is awesome with good ambient/downtempo music.
Ketamine + LSD - The key is to drop the acid, and wait ~3 hours to reach the peak. Once on the peak, snort, or inject the ketamine. One potentiates the other about 10 times, and the results of this combination is something new that doesnt reminds one of either ketamine nor LSD. I personally like ~400 ug of LSD, and to inject ~80mg of K. Remember that if K is to be injected, it should be the pharmaceutical, pure ketamine, that comes in vials, proper for injections, and not those unknown powders sold on the streets.
GHB and Cannabis - I think it's awesome, because GHB lifts your mood so much, and gets in an amazing synergy with the cannabis, which prevents you from getting too sleepy or slow, as sometimes happens with cannabis. It also makes you much more sociable than cannbis alone would do, as for my particular case, cannabis alone is pretty antisocial.
Other combos were already mentioned above.