You could use the History API rather than a hashbang approach?
- It allows you to manipulate the URL displayed to the user.
- It means that back / forward work sensibly.
- Bookmarking the page works sensibly.
- It's better in terms of performance, because if the user refreshes a page (or hits a link to the page from an external source) the correct content is loaded first time rather than having to load a blank page and then grab the correct content via AJAX.
The downside is that older browsers will not support it. You could fall back on a hashbang approach (if you really have to). I don't know of any existing frameworks that do this though. I would prefer to fall back on not dynamically loading content (i.e. full page reloads when the user clicks a link). The history API will become more and more widely supported, so this "problem" will reduce over time.
Here's a working example with some documentation. From the address bar, it looks like pages are loading "old school" (full page refresh) but if you take a look at the console (Firebug, Chrome dev tools), you can see that the content is being grabbed via an AJAX request.
Mozilla has some docs about it.