PingMate.jp has compiled a list of very useful and must have WordPress plugins. I installed most of them right after reading article. Following is the list of plugins.

1. WP Shortstat
2. Get Custom
3. WP Cache Inspect
4. Markdown
5. WP Pagenavi
6. Akismet
7. WP Related Entries
8. WP Contact Form

You can read the entire post here.