Top WordPress plugins can help you improve your site speed by optimizing and compressing images on your website.

1. WP Smush: This plugin automatically compresses images as you upload them to your website, reducing file sizes without losing quality.
2. EWWW Image Optimizer: This plugin optimizes images by reducing file sizes while maintaining quality, and also has the ability to optimize images that have been previously uploaded to your website.
3. ShortPixel Image Optimizer: This plugin can compress and optimize images, including JPEG, PNG, GIF and PDF files, it also can optimize images that have been previously uploaded to your website.
4. Kraken.io Image Optimizer: This plugin optimizes images by reducing file sizes while maintaining quality, it can also optimize images that have been previously uploaded to your website and it also provides a web interface to optimize images.
5. Compress JPEG & PNG images: This plugin optimizes and compress images by reducing file sizes while maintaining quality, it can also optimize images that have been previously uploaded to your website.

These are just a few examples, and there are many other similar plugins available. You may want to try out a few and see which one works best for your website.