Journal Impact Factor
The impact factor is an indicator of journal quality. A measure of the frequency with which the "average article" in a journal has been cited in a particular year, the impactor factor is calculated by dividing the number of current citations to articles published in the two previous years by the total number of articles published in the two previous years. Ultimately, the impact factor will help you evaluate a journal's relative importance, especially when you compare it to others in the same field.
ISI Journal Citation Reports (JCR Online)
Click on the "select a database" tab, and then the "Journal Citation Reports" tab. Select the "JCR Social Sciences Edition." You can browse a group of journals by category (e.g. "Communication), search for a specific journal, or view all journals.
Ulrich's Periodicals Directory
You can look for 'refereed' indicator, circulation statistics, and included abstracting/indexing services for a good indication of a journal's impact.
The number of libraries owning a journal is an indication of the impact and importance of the journal. Go to 'advanced search' and search by title or ISSN. Look at the 'libraries worldwide' link.
Citation Analysis or citation tracking is a way to see the impact of an article in its field. Also, it's a great way to use a "landmark" or influential article to find more recent, related articles that cite the landmark article.
ISI Web of Science
Select the "Web of Science" database. Then use the "Cited Reference Search" link to find articles that cite the work(s) of an author. Use the format [Last Name First Initial*] (e.g. Smith H*).
Go to "advanced search" and use the "references" field.
Sage Journals Online
Click on "advanced search" and select the "References" field from the drop-down box.
Search results that have been cited by others will have a link that says "Cited by [number]." Click that link to go to the citing authors. Use Google Scholar to find articles from a wide variety of academic publishers, professional societies, preprint repositories and universities, as well as scholarly articles available across the web.