Startup:
~ Most people work longer hours by choice
~ Things change fast, both corporate structure and business direction
~ You wear many hats if you want. This was a good thing for me. I could weigh in on product decisions along with doing development and it was more exciting.
~ Everything seems a lot more relaxed. You might not have HR for a while. More taking risks.
~ Usually a bit lower salary, although I think that depends more on how you negotiate.
Corporate:
~ There's usually a process for everything. This can be nice when it works for you but is also harder to change.
~ It's harder to make an impact on the business as an individual.
~ Pay is probably a little bit higher.
~ Great perks.
~ Team organization doesn't change as much. Less opportunities for advancement.
Things are very slow to change here. People who have been at the company 20-50 years are very fixed in their ways. People don't work as hard compared to the startup. I feel like a large part of getting promoted is just being here a long time. People don't do much development "stuff" outside of work, e.g. on my team of UI developers I'm the only one who has touched jQuery, Backbone, or Angular (work just uses Dojo).
People don't seem to be hungry here.
Now I work for a startup with about 15 employees as a front end developer and it's really great, I have almost complete creative control over what I do, the atmosphere is friendly and inclusive and we have a helter skelter in the office ;)
It depends what you're looking for, if you're happy to go to work and not be challenged, or have the majority of the company not know what you do, work in corporate. If you want to be part of a smaller team, be challenged daily and be appreciated, work in a startup.