I found this over at MobileRead. I don't have a Wii myself, so I can't comment on how well this works:
On a whim, I used the Internet Channel on my Wii to access the ePubs I have uploaded to Bookworm. Not only can I access them, but reading them was a pretty pleasant experience.
Then I tried the free chapters Baen put on their website - yep, a pleasant read.
Cool, I can read books on my TV! Not sure why I would want to do that, but still neat