1. Subscribe to Comments by Mark Jaquith: This plugin allow your visitors subcribe to individual posts of you blog, allowing them to receive notification via email whenever someone leaves a new comment on the post.
2. ShareThis by Alex King: ShareThis allows visitors to share content through email and popular social bookmarking services such as Technorati, del.icio.us, and Digg. It is a plugin that combines an “email this” plugin and social bookmarking service.
3. All in One SEO Pack by uberdose: All in One SEO Pack helps you finne-tune your blog by creating optimized titles and keywords for your individual posts automatically.
4. WP-DB-Backup: This is a plugin that provides easy method of creating a backup of your wordpress database. It allows you to schedule regular hourly, daily, or weekly backups and have those backup files emailed to you.
5. Google XML Sitemaps by Arne Brachhold: This plugin allows you to create Google-compliant site map of your blog. Whenever a new post or page created, the sitmap is updated and submitted to major search engines.

WordPress Gallery Plugins:

1. NextGen Gallery by Alex Rabe
2. Organizer by Imthiaz
3. Random Image Widget by Marcel Proulx
4. Mini-slides by Roland Rust

Related posts:

1. Using WordPress with Facebook: The Top Ten Plugins to Make it Easier
2. Use Twitter to Promote your WordPress Blog: The Top Six Plugins
3. 5 WordPress Plugins to add Professionalism to your Blog