This is a great, simple recipe that will also let you learn about roasting vegetables and the rich flavors that come from roasting.
http://food52.com/recipes/16467_roasted_celery_soup

I made a fabulous soup the other day. I used some of my homemade stock (but store bought would work), a can of plum tomatoes hand crushed and thrown in, carrots, onions, celery sauted and thrown in, parsnips, potato, kale, gluten free tiny corn noodles and a handful or two of red lentils. I put in about 1/2 to 1 tsp of cumin, some fresh thyme, rosemary and parsley (at the end for the parsley), and salt and pepper.

Pea soup is pretty easy. You can use stock or water, split peas, ham bone or ham hock (smoked or not), carrots, onion, potato, salt and pepper, cook until peas are falling apart. I like it pureed, but you can eat it without pureeing it or puree part and leave part. It's all good.

The suggested potato leek soup is also easy and very good.

Tomato soup. Find a recipe that uses canned tomatoes and serve with a grilled cheese sandwich.

http://www.food52.com/recipes/11904_broccoli_apple_soup

Simple, delicious, and just got mentioned in the New York Times. Also very flexible -- does well with substitutions. I always find it helpful to read the comments made on a recipe to see what other people did.

This one is very simple and also very good:
http://www.food52.com/recipes/15829_garbanzo_bean_soup_with_a_twist

Lentil soup!
Cook up some lentils (with some smoky ham to be awesome) and add stock. Done.
Just be careful you don't let your lentils go to mush.

Leek and potato. Here's a simple recipe:

http://simplyrecipes.com/recipes/potato_leek_soup/

You don't have to use chicken or vegetable broth. I usually use plain water and let the taste of the vegetables shine.