Suggest similar titles is module to avoid duplication of titles for all content types. At node add page when you are done with title, this module compares node titles of same content type and suggest you that one title matching with this title already exists in database. This helps the admin/user to avoid duplication of content at site. Admin can define what percentage of matching words should be suggested as duplicate title.
It provides setting page where following settings can be made:-
Enable this feature for any content type(s)
Enter ignore keywords in title comparison
Select maximum number of titles to show up as suggestion
Select whether this module should consider node permissions before displaying node title as suggestion
Enter percentage how exact the system should compare the title. For example, if you enter 75, then at-least 75% matching title will be considered similar
Display settings for suggested similar node title. It can be above or below title field
This module has template file to theme the suggested content as per requirement/design
There is another module uniqueness which can also be used to avoid duplicate titles. But following are points uniqueness is not offering but this module: