I think this is the module that you are looking for....
Better Exposed Filters
The Better Exposed Filters module replaces the Views' default single-
or multi-select boxes with radio buttons or checkboxes, respectively.
Description fields and Select All/None links can be added to exposed
filters to make for a better user experience.
Views Filters is a powerful tool to refine the results returned by a
given view. When you expose a filter, you allow the user to interact
with the view making it easy to build a customized, advanced search.
For example, exposing the node type field as a filter lets your site
visitor limit their search queries to just blog entries. Better
Exposed Filters gives you greater control over the rendering of
Why use this module? Because it provides a better user experience than
the default option. Try telling a client that they should click on an
option, then scroll to the next option and ctrl+click on it. Don't
just click 'cause you'll lose your first selection. Oh, and ctrl+click
again to unselect an option... Yeah, not user friendly.