After Internet Explorer we have been waiting for very long time for some other browser vendor to release 64bit version for Windows. The browser in question is Opera 12 with 64bit (or x64) versions for both Windows and MacOS.
This Opera 12 release is still in beta phase, so I wouldn’t recommend using new 64bit Opera 12 as default browser just yet. Opera says they’ve been waiting for ability to run all plugins under 64bit environment, while I personally don’t care a lot about Flash plugin I do applaud their effort to enable 32bit plugins to run under 64bit browser. This is now possible with the out-of-process plug-in architecture.
As you probably already know 64bit apps can allocate more memory, so Opera will also have more freedom in allocating memory. I think Chrome could definitively use this functionality.