hi,
I am a web designer in intermediate level. I want to some certification in web designing. Will W3 schools(HTML Developer certificate) or CIW certifications help me? or any others which will improve my market value?

I would think it would help you out in selling your services. If someone was trying to decide between your firm and someone elses firm. They would probably pick you because of the certification.

CIW one doesnt look to expensive either.

Certifications probably aren't going to be a huge help. EXPERIENCE counts for more in the web design business - at least as far as I'm concerned. You could have a certification and ZERO experience, but that doesn't make you a good web designer !

You can have a qualification and lots of experience, and still be a bad web designer!