I recommend this as a first (and possibly only), easy to install step to significantly speed up your site
WP Super Cache
Unlike WP-Cache 2, WP Super Cache does not use any PHP processing and serves static pages with URL rewrite rules on web server level. In a traditional Apache setup this does not help with memory usage but due to not using PHP more pages can be served on the same hardware.
Differences between WP-Cache 2 and WP Super Cache:
- WP Super Cache requires that you have Permalinks ON
- WP-Cache 2 works with both Permalinks ON and OFF
- WP Super Cache may require manual edits
- WP Cache 2 usually installs automatically without manual intervention
- WP-Cache 2 makes your site very fast, and can handle a ton of pageviews
- WP Super Cache makes your site very fast, and can handle even more pageviews
The above mentioned plugins don't solve another issue of typical Web 2.0 sites, including WordPress Blogs, though: A theme might have a dozen extra CSS and JS files all by itself, and every plugin might add another 1-5 so you'll end up with 20, 30 or even more extra files that need to be loaded before your site is ready.