I would like to purchase one of the following models:

PANASONIC AG-DVX100B
PANASONIC AG-DVC30
SONY DCR-VX2100
CANON GL/2

Right now I record sports events but I would like to transistion and film short docs some time in the future. I would like to have a camcorder that I can grow into and not have to replace in a year.

While you still can, you might want to edit your original post to make it clear that you'd like advice from people who have REAL experience with, and have produced something (anything) with, at least one of the cameras you've listed.

Otherwise, you'll be getting feedback from kids with cheap camcorders who SAW one of those cameras in a store once but have lots of strong opinions about which single one is obviously the best.

adidas,

Those are all great camcorders. They all have their good points and bad points. There is also about a $1500 difference between the least expensive and most expensive.
If you want some user opinions, you should check out Dvinfo.net
They have a great deal of info from users regarding all of those models.
Also check out the "Dv for the masses" forum. They have a lot of videos that were made with those models.
You may want to narrow it down by what options are most important to you. The biggest advantage to the DVX100B is that it can shoot in 24fps. If that's not important to you, you can probably cross it off since it's $800 more than the VX2100. (You get the idea)
Let us know some more info and maybe we can help some more.