Code:
##### Re-directing Begin #####
Options +Indexes +FollowSymlinks
RewriteEngine on
RewriteBase /
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /.*index\.php\ HTTP/
RewriteRule ^(.*)index\.php$ /$1 [R=301,L]
RewriteCond %{HTTP_HOST} ^yourdomain\.com$ [NC]
RewriteRule ^(.*)$ http://www.yourdomain.com/$1 [R=301,L]
##### Re-directing End #####
##### Friendly URLs Begin #####
Options +Indexes +FollowSymlinks
RewriteEngine On
RewriteBase /
RewriteRule ^story/([0-9]+)/?$ story.php?id=$1 [L]
RewriteRule ^story/([a-zA-Z0-9-]+)/?$ story.php?title=$1 [L]
RewriteRule ^(all|pligg|category1|category2|category3)/([a-zA-Z0-9-]+)/?$ story.php?title=$2 [L]
RewriteRule ^recommend/([a-zA-Z0-9-]+)/?$ recommend.php?id=$1 [L]
RewriteRule ^category/([a-zA-Z0-9]+)/?$ ?category=$1 [L]
RewriteRule ^category/queued/([a-zA-Z0-9]+)/?$ shakeit.php?category=$1 [L]
RewriteRule ^shakeit/([a-zA-Z0-9]+)/?$ shakeit.php?category=$1 [L]
RewriteRule ^story/([0-9]+)/editcomment/([0-9]+)?$ edit.php?id=$1&commentid=$2
RewriteRule ^story/([0-9]+)/edit/?$ editlink.php?id=$1
RewriteRule ^story/([0-9]+)/modify/([a-z]+)/?$ linkadmin.php?id=$1&action=$2
RewriteRule ^user/([a-zA-Z0-9-]+)/([a-zA-Z0-9-]+)/?$ user.php?login=$1&view=$2
RewriteRule ^user/([a-zA-Z0-9-]+)/?$ user.php?login=$1
RewriteRule ^search/([a-zA-Z0-9-]+)/?$ index.php?search=$1
RewriteRule ^login/?$ login.php
RewriteRule ^login/([a-zA-Z0-9-]+)/?$ login.php?return=$1
RewriteRule ^login/([a-zA-Z0-9-]+)/([a-zA-Z0-9-]+)/?$ login.php?return=$1/$2
RewriteRule ^register/?$ register.php
RewriteRule ^user/?$ user.php
RewriteRule ^topusers/?$ topusers.php
RewriteRule ^topstories/?$ topstories.php
RewriteRule ^about/([a-zA-Z0-9-]+)/?$ faq-$1.php
RewriteRule ^shakeit/?$ shakeit.php
RewriteRule ^submit/?$ submit.php
RewriteRule ^bugreport/?$ bugreport.php
RewriteRule ^rss2/?$ rss2.php
RewriteRule ^rss2/([a-zA-Z0-9-]+)/?$ rss2.php?status=$1
RewriteRule ^trackback/([0-9]+)/?$ trackback.php?id=$1
RewriteRule ^profile/?$ profile.php
RewriteRule ^admin/?$ admin_index.php
RewriteRule ^tagcloud/?$ cloud.php
RewriteRule ^tagcloud/range/([0-9]+)/?$ cloud.php?range=$1 [L]
RewriteRule ^tag/(.+)/?$ index.php?search=$1&tag=true [QSA,NC,L]
RewriteRule ^sneak/?$ sneak.php
RewriteRule ^pliggadmin/?$ admin_index.php
RewriteRule ^logout/([a-zA-Z0-9-]+)/([a-zA-Z0-9-]+)/?$ login.php?op=logout&return=$1/$2
##### Friendly URLs End ##### Red - these lines can cause problems on some servers, remove if errors occur.
Green - add in all your category names in place of "category1|category2" etc.
Blue - if putting pligg into a sub-directory of a domain, add the path in (eg. if installed in yourdomain.com/pligg - line would read RewriteBase /pligg/)
Purple - optional, helps consolidate google page rank, add in your domain name where required. Doesn't affect friendly urls, therefore entire "Re-directing" section can be deleted if wanted.