What is Technorati? It's a site that collects information placed in blogs and then creates indices of the information as well as rankings for the blogs within its system (which total in the millions). If your blog is not listed at Technorati, then you need to get cracking and get your blog in Technorati's sights. It's a big deal.
For Twitter, tags go by the name "hashtags" and you can find a listing of popular hashtags at Hashtags.org - but this site is different than Technorati's Tag Index. Here, you enter a hashtag, and the site returns with information on how popular it is ("trending"). Look at the percentages on the left: if they're low or nonexistent, then choose a different word for your hashtag. (For more on how Hashtags.org works and why it's a big deal, read the informative article provided by TwitterTipsCentral, "Where To Find A List Of Twitter Hashtags ".)
Tip: Create Your Own Index of Tags
And, remember that tag. No need to reinvent the wheel. If you regularly publish items dealing with dogs, or beer, or recipes, or speaking Klingon -- whatever your focus -- collect the most popular tags for that topic and save them. Make your own list of tags for your use, as a ready reference.
Why should you care about tagging? Read my earlier post, "Twitter Tip: What is a Hashtag?" for details on why tags are a good thing.