If you are a twitter user, you should check out the application TweetDeck! It shows you multiple hashtags at one time in one screen. www.tweetdeck.twitter.com

BagTheWeb http://www.bagtheweb.com/edu For any topic, you can create a "bag" to collect, publish, and share any content from the Web. Beyond most social bookmarking or curation tools' capability, BagTheWeb enables users to build networks of bags. This way bags can be linked together to provide rich and complete information about any topic.
Delicious https://delicious.com/
Blendspace https://www.blendspace.com/
LiveBinders http://livebinders.com Organize your favorites into "binders" with tabs and sub-tabs and share or embed those binders.
Pinterest http://pinterest.com Pinterest is a site where you can "pin" (or collect) photos you find on the internet. The photos link to the webpage or blog post where the photo is located, so you can read more about it.
Standards Toolbox http://www.standardstoolbox.com/
Symbaloo http://symbaloo.com Is a highly customizable graphic page with "tiles" creating a "webmix." Share your webmix or use those others have put together.
Zite http://www.zite.com/ Zite is a personalized news editor to help you keep up to date on the latest news (you choose your topics--current events, science, tech, etc)