SW+ Stargate! Saberpike wielding gua'uld (please excuse N008 spelling.)
Rakata Ancients!
Jedi Master Teal'c!
To parrot JEStusker: This has been loosely done already. At the time of the original post it had been at least referenced once in the Book of Sith (which came out 2 years prior to the post), on pg 102 "The Kwa built Infinity Gates to travel to other stars..." which sounds pretty dang close. But I'm in full agreement that would be a great mash-up.
Also love the posts about SW+TWD, with apparent literary references. Now I must read those 2 books. Although I fear that would be the most devastating thing to happen in the SW universe and could truly lead to extinction of all life therein. Case in point, the inaccuracy of blasters. Once the infection spreads past a certain point the zombie apocalypse spells doom since who the heck can score headshots religiously with blasters? Although my beliefs on the matter must be somehow mistaken in their doomsday results since this has also been done already in SW. Again referenced in the KOTOR and also in the Book of Sith pg 43 "Reanimated Dead...(were created by the Sith Dathka Graush using a technique where)...it was he who melded alchemy and spellcasting to perfect necromancy." "animates...the freshly dead...transforming them into an unstoppable legion impervious to pain and able to transmit a necromancy infection by biting." Still I agree this would be awesome to see in a fanfiction movie or something where a Sith finds his holocron and wants to test the effectiveness of these troops on a rival or some innocent planet, destroying it (and likely dying in the process rendering the holorcon lost, to preserve SW universe/EU canon).
For my addition to the topic, I suggest the mix of SW+Mass Effect:
A seemingly obvious choice for the rich cultural diversity of alien species, and bridging the gap between a version of our solar system/galaxy and SW galaxy in a believable way and allowing us to have enough technology to participate actively. Easily doable by some random in SW stumbling upon and activating a dormant Mass Effect Relay opening the door for this possibility. I'm highly sure someone has done some fanfiction somewhere along these lines already in all likely hood. But it'd make for an epic tv series, netflix movie series, or videogame mash up RPG.
I almost forgot, I love the idea mentioned of SW+DBZ from the perspective of Saiyans being manipulated by the Sith to attack Republic worlds. Heck Frieza uses telekinesis and operates like a Sith Lord building his empire while hating sharing power. But a full on battle scene between a transformed Saiyan and several Jedi would be amazing too. Since it'd be impossible to deflect energy blasts of that size with lightsabers, and they'd have to work together to eventually figure out how to sever tails using lightsabers. I see shaking your head at how stupid it could be, but so many possibilities. Including Z fighters teaching small sects of Grey Jedi the Bakku Jutsu (the flying technique) would be over the top but hilarious. Let alone a Jedi competing in the World Martial Arts Tournament in DBZ.