I'm using subversion to make the process of updating wordpress easy (installing an upgrade is a simple `svn update`). To extend that simplicity to plugin management, I'm using the svn:externals property to automatically update my plugins. Installing it is simple: `svn propset svn:externals -F externals .` My externals file looks like: 
advertising-manager http://svn.wp-plugins.org/advertising-manager/trunk/
akismet http://plugins.svn.wordpress.org/akismet/trunk/
amazon-showcase-wordpress-widget http://svn.wp-plugins.org/amazon-showcase-wordpress-widget/trunk/
google-analyticator http://svn.wp-plugins.org/google-analyticator/trunk/
google-sitemap-generator http://svn.wp-plugins.org/google-sitemap-generator/trunk/
google-syntax-highlighter http://svn.wp-plugins.org/google-syntax-highlighter/trunk/
latex http://svn.wp-plugins.org/latex/trunk/
smart-archives-reloaded http://svn.wp-plugins.org/smart-archives-reloaded/trunk/
stats http://svn.wp-plugins.org/stats/trunk/
wp-rdfa http://svn.wp-plugins.org/wp-rdfa/trunk/
xrds-simple http://svn.wp-plugins.org/xrds-simple/trunk/