What CSS3 features still need vendor prefixes?

Solution 1:

Use the site http://shouldiprefix.com. It has the single purpose to "show what prefixes are needed for a newer CSS property."

Just enter the property you're interested in the search field, and it will return something like the below graphic:

enter image description here

Solution 2:

There is a great site which allows you to check out support of any css property by most modern browsers. It also shows info about vendor prefixes (if they are needed). This site is named "Can I use" - http://caniuse.com