I haven't tried these yet so I can't speak from experience but the local company I'm ordering my seeds from had a couple bush type summer squash.

http://www.victoryseeds.com/squash_zucchini_dark-green.html
http://www.victoryseeds.com/squash_early-prolific.html

It felt like they had quite a few options that were well suited to container gardening so I'm excited to get things growing. This is going to be my first year with actual planning and not just grabbing stuff from the store and throwing it in pots.

Eight Ball, Cue Ball, or One Ball are round zucchinis of bush variety that grow well in containers. There is also a new variety of Zucchini called Astia, which is a patio, dwarf variety that is being specifically marketed for container growing. Seeds can be found at Renee's Garden Seeds.

Bush varieties of any squash, including the crookneck and straightneck varieties of yellow squash, are what you are looking for rather than the rather larger sprawling, vining types.

Susan