I'd go against the stream and advise against caching plugins. I used to use them but after several tests by different tools I found out that the blog runs faster without those plugins. Instead, you could reduce the page size, I mean the media stuff you have. For images you can use smush.it as suggested above. Badly written codes can cause longer load times and therefore you should choose popular plugins from popular developers for your necessities.
If you've worked the blog a lot then as you may have noticed, posts and pages are saved as revisions and those can slow down loading time in admin panel, there's a database optimization plugin to delete them (and keep the actual post), that helped a bit for me.
Try to keep the amount of plugins minimal, only use ones you absolutely need.