Facts off first 
The PMA next year is held March 3-5, Las Vegas.
A note: this is pure speculation from a Canon user who follows news, announcements and rumors closely. I don't claim to have any insider information whatsoever. If you are looking for juicy info from "a friend of mine at Canon", or "a sports photog told me", this ain't the thread I'm afraid. 
What can we expect from Canon at PMA 2009?
Historically, the trend for Canon is to announce ONE new body at PMA events. Previously, they announced:
2008: 450D
2007: 1D Mark III
2006: 30D
2005: 350D
2004: 1D Mark II
2003: 10D
Canon currently has six DSLR tiers, the latest models in each are:
1000D
450D
50D
5D Mark II
1D Mark III
1Ds Mark III
Let's look at the possibilities:
The 50D and the 5D Mark II have just got announced, nothing new is going to happen here.
The 1000D was announced in June, it's likely we'll see an upgrade in 2009, but PMA seems too early.
The 1Ds Mark III will be 18 months old at PMA, I think an upgrade this early is unlikely, especially that there are better candidates.
The 1D Mark III will be 24 months old at PMA. Given its well documented problems with AI Servo, and the success of the Nikon D3 in the sports community, it's possible Canon might give it an earlier upgrade than the initially planned cycle. Possible upgrades would be: a new sensor based on the tech used in the 50D and the 5D Mark II with a megapixel bump, DIGIC IV, HD movie mode, working AF this time
and a better LCD. Whether this camera would be called a 1D Mark IV or 1D Mark III N depends on the number of upgrades, I think a new sensor would definitely warrant a new Mark number (as in the case of the 1D Mark II N, it retained the sensor and the shooting speed of its predecessor).
The 450D will be 12 months old at PMA. Historically, this line had upgrades every 18 months, however, Canon broke this pattern with the 50D this year, so it is possible they would change this line to a 12 month cycle. The 500D would counter Nikon's D90 (which I expect to sell just as well as the D80 did), and Sony's possible upgrades to the A300 or the A350. Just as the Nikon D90 has it, I fully expect Sony to put HD movie mode in at least one of these cameras (Sony being a major player in the film business this looks like a natural move). The 500D would then have the latest sensor technology with a megapixel bump to 15 MP, DIGIC IV, VGA LCD and the movie mode of course.
Apart from the six current lines of DSLR bodies, there's always a possibility of Canon opening up a 7th tier. One much talked about camera would be the 3D, which would have a more professional AF than the 5D Mark II, and a higher framerate. Personally I think this is just wishful thinking at the moment, and even if it might happen eventually, I don't expect Canon to announce such a camera at this year's PMA.
As for my wrapup, this post would not be complete without a proper prediction for next year, this is what I expect (just don't quote me on it
)
January/PMA: 500D
Summer: 2000D
Autumn: 1D Mark IV
Lenses?
I really have no idea. The lens division is notoriously hard to predict. Every year the usual suspects are wound up (you know: 24-70L IS, 100-400L IS upgrade, 400/5.6L IS etc.) and Canon have ignored these so far, so it's anyone's guess really.


