While searching the Web I found a similar validator to well known w3.org validators - it's XHTML-CSS Validator. Actually, the original validation is performed by w3.org validators.
What's so good about it? It validates both XHTML and CSS in one click. Like w3.org validators, it provides you "valid icon" if URL passes the validation.You can use advanced validation and choose diferent XHTML and CSS settings for validation. For example, you can choose CSS version, encoding and so on.
If you are using Firefox, you can download and install BeValid! extension that let's you validate websites as you surf just by clicking on toolbar button. Unfortunately, it cannot validate local websites and therefore can't be used during the development. It would be good to see that feature soon, as well as extension for Interner Explorer.