Don’t know about a plugin, but you can delete the code that says <?php get_sidebar ?> in the page files that you don’t want a sidebar in. Those files are page.php for pages, single.php for single posts and there’s also archive.php and archives.php that you might need to compare to figure out which one is which (if you even have both).
You could copy wp-content/themes/your_theme/page.php into page_no_sidebar.php and then remove the <?php get_sidebar(); ?> tag from this page template. Also remember to name this template by adding the required comment lines at the top of the file. I don’t remember all the details.
When you create/edit a page, choose this template.
http://codex.ww.wp.xz.cn/Stepping_Into_Templates
