Yes, you can purchase extenders that connect by Ethernet, and that is better than the plain wireless units. You can also use inexpensive wireless routers and set them up as extenders. The instructions have been posted here many times, but if you cannot find them I can repost later.
I do have an extra wireless router, but it's not supported by dd-wrt (it is one of those infamous Linksys wrt54GP2 routers that Vonage was giving out).
I'm trying to find which extenders use the ethernet port as the extension instead of the wireless signal. Do you have any links to any of these extenders?