I nominated four anime that I, personally, think about crossing over in various ways all the time. Two of them (the ones with the pointless semicolon punctuation) are in the same universe but do not have broad canonical overlap. The four I have nominated are:

Steins;Gate
Robotics;Notes
Mahou Shoujo Madoka Magica | Puella Magi Madoka Magica
Fate/stay night & Related Fandoms

Assuming I will be able to participate, I also hope to offer and request some live action/western fandoms, too, but most of those I might be interested in appear to already be nominated. Does anyone have any that they don't have room for that they really want nominated? I could be persuaded to even if I don't really know them to take up one or two of my extra spaces while I brainstorm.