Sitebulb charges 149 dollars a month to visualize how internal links distribute PageRank across your site. This does it in the browser - crawls your sitemap, computes PR, renders the graph as SVG, flags orphans and hubs.
Read the story behind this tool: Why I built this - the link graph visualizer Sitebulb charges for.
Related: Mega SEO v2 site-wide crawl / Performance tool stack