I travel & work in up to 25 states in a year but the company that pays me is in CA and I live in FL. Who's state tax do I pay? CA, FL, or all the states I worked in?

Are your a W-2 employee? What state does your W-2 indicate in box 15.

The official answer is you pay all 25 states, but "nobody" does. See http://money.cnn.com/2013/06/28/pf/taxes/business-traveler-tax-threat/

I haven't gotten the W-2 yet, but in the past they took out CA state taxes. This year they have taken out no state sales taxes on my check. I live in FL (no state income tax) so if they have FL in box 15, do I have to pay any state sales tax? The reverse, if it shows CA do I have to pay CA state tax?

"Have to" are the key words.
It depends on how aggressive CA wants to get. If CA is in box 15, you'll have a hard time not paying CA tax.  If FL is in box 15, you should not need file a CA return. BUT, since CA has you in their database, from previous years, you may hear from them.
What are the rules? You should file a CA return and pay tax on only the income your earned while physically in CA.. But since you have a home state without an income tax, CA could get aggressive, especially since much of the other income was not earned in your home state.  The rules further say you should file returns and pay taxes in those other 24 states, in which case an aggressive CA would/should allow you a credit.

So, wait and see what the W-2 says.

Thanks. Good info.