Take the email below from Paperless Post, for example. I love the header of this email: It provides a clear CTA that includes a sense of urgency. Then, the subheader asks a question that forces recipients to think to themselves, "Wait, when is Mother's Day again? Did I buy Mom a card?" Below this copy, the simple grid design is both easy to scan and quite visually appealing. Each card picture is a CTA in and of itself -- click on any one of them, and you'll be taken to a purchase page.
We also love how consistent the design of Uber's emails is with its brand. Like its app, website, social media photos, and other parts of the visual branding, the emails are represented by bright colors and geometric patterns. All of its communications and marketing assets tell the brand's story -- and brand consistency is one tactic Uber's nailed in order to gain brand loyalty.