Three Things I Would do to Prepare for WotLK...  

... If only I had the time.

I fully plan to race to 80 with Dezdemone. I will have plenty of time to enjoy the journey while leveling my other two 70s as well as the death knight and druid that I plan to get to max level during Wrath. With that said my pre-expansionary goals are aimed specifically at a full blown all out no holds barred race to 80.

1. Deal with my bank.
This may be the most obvious thing, and it's something I expect most people will work on while we're still in BC. I plan to clear out items that I am unlikely to need in Wrath. For example SSC and TK only health potions. I also would like to have a cash stash of at least 10k gold. Not having to worry about the cost of respeccing and repairs will help in my quest to zing to 80.

2. Find or write a guide on how to level to 80.
I would like to know where I am going and how to do all the quests so that I can plan my route. I would also like to know now what items I should be farming in preparation for release. For example there's at least one Quest where an elixir of underwater breathing would be nice. Having a list of things like that will allow me to put those items together now and will save me trips to the AH while leveling.

3. Research all known crafting patterns (Particularly Plate Tanking Armor) so I know what not to sell, give, or throw away while leveling.
If I know that big slugs drop slug scales and I need 15 slug scales for an epic breastplate I will make certain I do the quests that involve those slugs.

All these things are currently on my "To Do" list. I plan to get as much done as I can before WotLK, but unfortunately school does come first.