These 4 sites offer free Bootstrap themes, snippets and extensions.
Bootstrap official website to download bootstrap framework, tutorials and jquery plugins. You can download your own customized version of Bootstrap.
Also it provide
You can also submit you own twitter bootstrap resources here.
Bootswatch is a best source to download new bootstrap themes. It provide open source theme file (.css). So download a CSS file and replace the one in Bootstrap.
LayoutIt – Bootstrap 3 interface builder.
I see that there are many options to work with bootstrap
and you can add bootdey
Bootdey is a gallery of free bootstrap snippets