A solid, well-rounded company that's positioned nicely in this economy.
Pros
Working at Travelers has been a great, well-rounded experience. Working for a large company provides plenty of opportunity- both laterally (I've changed jobs and careers without changing the building I work in), and upwards (growth opportunities abound, if you're proactive enough). The culture is something that is hard to quantify, but makes working here a pleasure; the interactions I've had with (most) senior management has been positive, my immediate management is great, and my coworkers are a great bunch of people. Additionally, in this economic climate, it's reassuring to be with one of the strongest companies around- and the minimal dip in its stock price over the last 6 months has also been a nice-to-have. The benefits are good- but not great. There's a fairly generous PTO policy, and the 401k match is a nice 1:1 up to a certain limit (especially with many companies cutting this), but there are middle-of-the-road health and other benefits.
Cons
Similar to other large companies, Travelers can move slowly when it comes to adopting new technologies or making decisions. If you can work within and on the 'system' of the place, and accept that any company, large or small, will be political, it's not a real issue. Other than that, I don't see many other downsides.