What's the best container to take salad to work?

This is by far the best I've found.

http://www.amazon.com/Fit-Fresh-210-FF-Shaker/dp/B000FNEVQG/ref=sr_1_7?ie=UTF8&qid=1326140980&sr=8-7

I'm partial to the Clip & Close line from Frieling:

http://www.amazon.com/10-Ounce-Square-Shaped-Transparent-Food-Storage-Container/dp/B0006D37FQ/ref=sr_1_1?s=home-garden&ie=UTF8&qid=1326180841&sr=1-1

I love them because the seal is extra, extra tight, eliminating as much as possible any chance of dripping. They have both plastic and glass versions, I use the plastic versions.

Whatever you end up with, do keep in mind that if you go with a stainless steel container (they're becoming more popular by the day), acidic dressings can alter the taste of the salad or damage the container after interacting with the steel.

This might not be what you were looking for, but I've had luck with just a normal wide-mouth jar, like tomato sauce or salad dressing might come in, a la lifehacker: http://lifehacker.com/5857420/make-salad-in-a-jar-for-an-easy-grab+and+go-lunch-that-stays-fresh-for-days

I take my salad along in a ziplock bag with a paper towel inside to keep the moisture from sogging up the greens. I keep the various toppings separate and then when I get ready to eat I transfer the salad to a bowl for the meal, dress it and eat.

I use a stainless steel tiffin bowl

http://www.happytiffin.com/lunch-bowls.html

and a small jar (from minced garlic, I think) for the dressing. I just put the jar in the bowl with the salad for transport. No trash, no plastic.

Gladware containers makes a "To-Go" line; a container with a smaller container that fits in the round part of the lid from when they changed their design so lids snapped together. So they are inexpensive, easy to find (mine came from Target), only have one lid to keep track of, and if the dressing conatiner were to come knocked loose (has not happened to me) it'll just fall in the salad instad of making a huge mess. http://www.glad.com/products/food-storage/containers/glad-to-go-lunch/

I would second the gladware "to-go" line. I make a chopped salad every day for lunch, these work great. I've never had one burst, and I have significantly overfilled a few times.

 Take a look at this site’s ”Microwaveable Bowls with Handles” item, at http://kk.org/cooltools/microwaveable-bowls-with-handles/