What Margaret said. Brainstorm like crazy. If you have a relocation company, they probably have a checklist. Ask.
When I moved cross country last year, I had four main lists (all are Projects in GTD terms):
* Things needed to vacate location A. This list had stuff related to selling the house, packing the house, etc.
* Things needed for the move itself. Stuff like arranging plane tickets, health certificates for the cats, carriers for the cats, temporary lodging, etc.
* Things immediately needed in location B. Set up phone lines and Internet service, set up utilities, etc. Also business continuity stuff like notifying my clients of my new address.
* Longer term requirements for location B. Stuff to do after the dust settles, from buying furniture to finding a new dentist. For your sanity, move everything possible to this list, and treat it as a Someday/Maybe.
Second, delegate like crazy. Take full advantage of any relocation benefits your company offers: a good realtor or move coordinator is worth their weight in gold. Call in every favor you are owed. Hire people for every task that you possibly can. (If budget is an issue, throw money at the more urgent tasks first, then the more difficult tasks.) If you and your significant other find yourselves in different locations, split tasks by location and give the other person a free hand.
Third, when planning move-related downtime, take your best estimate, round up, and double it. My move went as smoothly as I could have hoped, and I was still out of commission for twice as long as I expected. This stuff just takes time. Similarly, make sure you have some free time in location A to say your goodbyes properly, and time in location B to find new special spots. Be as kind as possible to yourself: you'll need and deserve every bit of pampering you can squeeze in.