Core search, use wildcards by default
I've always used the Porter Stemmer module to handle that, it works a treat.

This module implements the Porter stemming algorithm to improve English-language searching with the Drupal built-in Search module.
The process of stemming reduces each word in the search index to its basic root or stem (e.g. 'blogging' to 'blog') so that variations on a word ('blogs', 'blogger', 'blogging', 'blog') are considered equivalent when searching. This generally results in more relevant search results.