1. Don't know of a standard way to do this, but there definitely should be.

2. group_tools may do this for you already.

3. bookmarks plugin bundled with core.

Evan, for 1. Isn't there an event/hook for river item creation? Also for 3. I think he wants something like AddThis integration.

I didn't. group_tools plugin doesn't. @Steve, I don't want content share plugin. I need a plugin like bookmark but mutch better.

1. There is a hook. See add_to_river().

2. Elgg 1.8.9 will include this option (it is in the 1.8 branch right now). The group_tools does not do this according to its feature list. 

is there any theme code like is_admin_logged or is_member_logged

elgg_is_admin_logged_in() . The API docs has a decent search, and most (but far from all) API functions now start with "elgg_".