There are many tools that you can use. My advice, don’t use online page rank checkers. They are very slow. Use desktop applications or FireFox plugins.
My favorite three Google pagerank checkers
- PaRaMeter – Fast and reliable desktop application. Works with proxies, extracts URLs (inner pages) and is free for use.
- SEO For FireFox – Tool you already know. Install, activate and type site:[domain name] to check pagerank of inner pages.
- SEOQuake Toolbar – Similar to SEO For FireFox, but you can also sort pages by pagerank.
P.S.: Google pagerank of “From Zero To SEO” inner pages (PaRaMeter screenshot).