1) I have a Suggestions tab by skribit.com for readers to suggest topics for blog posts. It's a sleek widget but sadly hasn't worked for my blog. I have never received any suggestions.
2) A View Random Post button. It ensures there is something to read even when I'm on a blogging holiday.
3) A Google translation widget. I found it better than Altavista's babelfish but it's still as poor as any non- human translator.
4) Top posts widget by PostRank to display the most popular posts on the blog.
5) A Random Multilanguage Word of the Day widget by Internet Polyglot just to show off my love for the languages. It displays different words in English translated into 17 languages.
And finally as everyone else suggests, a Google Friend Connect box.
That's all. Hope you found it useful!