What program/software you recommend (the best in the market) to manage multiple accounts for SEO?
It depends what you mean by “managing multiple SEO accounts”. If you mean manage multiple client projects, I’ve heard WebCEO is good for that, but I’ve only tested it briefly. I prefer to use a tailored Excel spreadsheet to keep track of client link data etc.
I also use Freshbooks to invoice clients and timesheet their services and ProposalKit to create client proposals.
I don’t recommend any specific tools to perform the site optimization itself – that should always be done manually if possible. There are however some useful SEO tools for determining or reviewing various aspects of the page/site optimization. SEO Book Tools and SEOmoz Tools spring to mind.
Also check out the tools category on Search Engine Wiki.