We are in the process of creating a web part that shows you all sub sites (that the logged on user has access to) under the current level in a tree view control. Similar to a site map.
Here is a preview of the web part. By default it shows the tree view control collapsed and you can click the nodes to navigate to the appropriate site.
We will be posting the package to our echo Technology site as a free download very soon so keep an eye for this.
If you are not already aware, we have a free sub sites web part that shows the current level of sub webs that the logged on user has access to.
You can get your free copy here