login-lockdown – protect your neck
nextgen gallery – great for internally managed photo galleries
tubepress – let youtube handle the bandwidth and conversion please.
eventsmanager (for RSVP type events)
gigpress (for musician-style tours)
capabilities manager – if you have multiple content editors with varying roles.
Mail From – change the default from email address and name.
exclude-pages – sometimes the main nav doesn’t need to be that cluttered
user photo – great for adding some personality especially with multiple content authors
maintenance mode – show users something professional while testing and updating
shadowbox js / lightbox PLUS – sexy photo/video presentation
advanced twitter widget – meh. it works well for client managed twitter feeds.
Register Plus – get all the info you can from your users
all in one SEO pack – what good is a site if no one finds it
kadom-ads-management – if you have savvy enough admins to manage their own ad space
wp super cache – great for high-traffic sites but can cause issues with some plugins
formbuilder – submits forms via email and to the db. export to csv. nice.
FeedBurner FeedSmith – if you’re into feedburner for rss feed management. This plugin works excellently.