I use WordPress SEO on almost every site I launch – WP Tuts+ has a series of tutorials on configuring the plugin that’s helpful. I’ve got a brief article here. I also use Yoast’s Google Analytics plugin as well.
If you’re looking for easier analytics with better eCommerce details, check out KISSmetrics. We have a guest post here about using it with WooCommerce. Google Analytics works well and is free, but can require a lot of setup for detailed event tracking (there are several eCommerce integrations available to help a bit). Mixpanel and Trak.io are a couple of other useful tools.
As for marketing tools, I like WPSSO to add relevant meta information for social sharing sites – this ensures that any content you or users share is as detailed as possible (cards for Twitter, images / video for Facebook, etc). I have a full review of the plugin here.
Optin Monster is also really helpful for building email lists to re-engage visitors and customers. It creates a popup that reminds visitors to sign up for your email list, which ensures that they don’t forget about you when they leave your site.