Google Wave has a lot of potential, and in many ways is already useful despite being in early beta. One problem I’ve seen with many people however is forgetting to check for new waves. Here are a few tools that can help.
Update 3/4/2010: Google has a new Google Wave notification by email feature that you should check out. Other tools are still listed below in case email isn’t your thing.
Google searches indicate that there may be a Windows Desktop notifier in the works, but I can’t confirm. If you know of any others please comment and I’ll add them to the list.