I love this asparagus soup:
http://www.epicurious.com/recipes/food/views/cream-of-asparagus-soup-creme-dasperges-104746

Make a Spot Prawn and chorizo chowder. With fennel, tarragon and ouzo you get a lovely flavour that entices. Potatoes and cream and yum.

sorrel soup, served either hot or cold. Julia Child had a good recipe for cream of sorrel soup. Would go well in a spring menu including salmon and rhubarb.

This red lentil soup is a great choice, and is filled with spring/summer flavors: http://www.healthline.com/health-recipes/allergy-friendly-curried-red-lentil-soup

And this Fresh Pea Risotto Soup is super simple and can easily be prepared ahead of time: http://www.healthline.com/health-recipes/fresh-pea-risotto-soup

Vichyssoise is nice for spring.

Ina Garten's Spanish Pea Soup with Crispy Ham. Very good,very easy.

Here are a couple more ideas:
https://food52.com/recipes/18052-eleven-madison-park-s-strawberry-gazpacho
https://food52.com/recipes/17595-creamy-spring-turnip-soup-with-wilted-radish-greens-and-bacon

I suppose it depends on what else is being served and what type of soup you're looking for...

To me, spring is about the fresh/green flavor. Here are a few that I've bookmarked and/or made.

https://food52.com/recipes/31438-anna-thomas-green-soup
https://food52.com/recipes/20641-crab-asparagus-noodle-soup
https://food52.com/recipes/26128-kale-ale-soup
https://food52.com/recipes/4180-cream-of-asparagus-soup-with-yogurt-and-tarragon