I'm looking for a low cost/free CDN that can serve my static files. (I will serve dynamic files from my own server)
From the plans it seems like free plan includes CDN:
https://www.cloudflare.com/plans
http://www.incapsula.com/pricing-and-plans/compare-all-plans/?src=176
But after registartion Cloudflare wanted me to change my DNS records to their DNS servers.
Is it not possible to serve some files from their server without changing DNS records ?
Is it not possible to serve some files from their server without changing DNS records ?
Correction: see comment above from xxdesmus
Not from CloudFlare, atleast not unless you want to serve the files from another domain. CloudFlare is a lot more than a simple CDN to serve static files, for example it's going to try and block malicious attacks to your site as well, and to do this it needs to be set as your authorative name server.
From a CDN point of view, the advantage for you with CloudFlare is that the caching is automatic (unless you overide this with custom page rules), so it's easy to set up.
If this isn't a good fit for what you want to do, there are plenty of other options where you can specify on a file by file basis which assets are to be served from a CDN. For most sites I manage, even using a paid service like Amazon CloudFront costs hardly anything.