Here is our list of chart-topper, speed-inducing plugins.
<ol>
 <li>Faster Rendering: WP Fastest Cache. ...</li>
 <li>Caching: W3 Total Cache. ...</li>
 <li>Compressing JavaScript &amp; CSS Files: WP Super Minify. ...</li>
 <li>Reducing Image Size: WP Smush. ...</li>
 <li>Decreasing Pageload: BJ Lazy Load. ...</li>
 <li>Optimizing the Database: WP-Optimize.</li>
</ol>

Plenty offer useful niche solutions, but few are truly must have WordPress plugins for all sites. No matter what kind of site you're running.