I use adwords keyword tool to get the keywords google considers synonyms.. You can also try ~keyword queries to find relevant keywords.
I agree w/ jitendraag. I simply use the ~ operator at Google. I set my preferences to 100 results per page first (actually mine always stays 100). Then if I want to know other keywords that are considered by lexical semantic analysis to be related to my keyword phrase "XXXXX YYYYY ZZZZZ" I simply search for ~XXXXX ~YYYYYY ~ZZZZZ and note all of the keywords that are highlighted in the search results. Or you can do it all at once by searching for: ~XXXXX ~YYYYY ~ZZZZZ Great technique to find alternate, related keywords that will still help your URL rank for "XXXXX YYYYY ZZZZZ" but will reduce the spamminess (new word?) of the page by reducing the number of times you have to keep repeating the exact same keyword / keyword phrase on the page.
I really believe in writing a real and quality text -and then you dond need even to know what LSI is.....
An interesting free one is http://www.quintura.com For example, if you type in "books" it will give you various related keywords, such as store, bestseller, browse, author interviews... The free Google keyword tool - https://adwords.google.com/select/KeywordToolExternal - usually gives excellent "additional keywords to consider", many more than you'll normally find at Quintura. You can also use http://thesaurus.reference.com . If you use all three, in total you'll probably come up with a lot more phrases than you could possibly use in one article. __________________ magento development
Also you can use Google's new "wonder wheel". 1.Do a regular search of any term 2.At the top of the page will the words "web" and "show options" (they are just below the google icon) 3. Choose "show options" 4. choose the "wonder wheel" option. 5. This will give you related terms