When it comes to making great espresso, it's all about the crema, the frothy white cap that's produced as a result of extracting flavor under (tons of) pressure. Most great espresso roasts are specifically formulated to yield great crema, and feature a generally chocolatey, mid-range flavor profile.
Some of our favorites include Espresso Blend
(Herkimer), Under Pressure Espresso
(Slate), and Locofocos Espresso
Something to be aware of, if you're out and about in cafes: there's a trend towards featuring single origin coffees as espressos. But by contrast to traditional espresso blends, single origins can yield super sharp, peaky flavors when they're brewed as espresso that aren't always what you'd expect, especially when served with milk.