Two cans and a piece of string fixes all problems.
Seriously though, just about any router out there these days is Wii-friendly.
I had this strange problem where I would get a disconnect error after every Strikers online series (not match, it worked fine up until that point). Turns out that I had a problem with TCP ports closing too early (which also affected MSN conversations and the like) and required access to the internal configurations of the router to fix it.
But now it all works.