The following URL's will take you to lists of plants known to be Toxic to cats. 

http://www.cfainc.org/articles/plants.html

http://www.moggies.co.uk/plants.html

http://www.ansci.cornell.edu/plants/index.html  

http://www.theanimalrescue.com/toxic.html

Please be aware that Easter Lilies are deadly to cats as are most plants in the genus lilium.  To learn more about just how deadly lilies can be visit the cfainc web site above.

These list some plants that are Non-Toxic:

http://www.cfainc.org/articles/plants-non-toxic.html

http://www.moggies.co.uk/nontoxix.html

These lists are by no means complete and cats should not be allowed to chew on any plant that is not specifically grown for them.