If I have a site that updates lets say 20+ times a day, what is the best way to let my members know about the updates without flooding they with emails?
By telling them to go to your site every now and then because you have daily updates. Ask them to put your url in their favorites or to bookmark it.
I was thinking of having it send out a email list everyday for the people that subscribe to it. But it may be sending out to many mails so I'm not sure if I want to do that.
That's why I suggested to to instruct them to remember your site, so you don't have to do that. But why not simply do it on a weekly basis, or, say, every 4 days? That's not too much. And do you really do that much updating??? You can also put a checkbox in your newsletter sign up box that reads something like: "Check here if you would like daily updates."
RSS feeds, in my opinion. Don't spam your feed, but make your visitors really aware that it's there. Include your RSS feed if you ever send your members emails. Sure, you'll have some that will just read it from their feed reader, but I think many will come to your website to post comments/check out other stories or whatever.