'Search Bookmarks' is a simple Chrome extension to search your bookmarks in Chrome omnibox. Type 'bm' and spacebar, then you can start to search bookmarks.
You can install this extension at chrome web store.
After I wrote this extension, I found that there is another extension named Bookmark Search which has the exactly same feature as this one. (even the keyword 'bm' was same). It has been there since Feb 2011. You can choose that extension over this. :)