This isn\'t directly a programming question, so I apologize in advance. I\'ve been working on a grammar-free random sentence generator for a typing game I\'d like to make, and I
MorphAdorner (Java) has a simple Verb conjugator (with online demo).
But if you are interested with an exhaustive listing you can check Lexical Tools' Inflection Variants. After downloading Lexical Tools, you will be importing the data to your database server. Then you can just query the database using their library (Java).
SimpleNLG also has this feature, and is very much related to Lexical Tool.