Here are my favorite TRS-80 links. This list has gotten a bit long, so I've now divided it topically. Many of the sites really span more than one category, but I've tried to classify each by its main topic.
You can subscribe to the TRS-80 Mailing List by sending email to trs80-request@cs.ubc.ca with the word "subscribe" as the message body (not the subject). Jeff Vavasour runs this list.