There are thousands of species of macro-algae. Here a few sample species:
http://www.reefs.org/hhfaq/pages/picture_pages/faq_sargassum.html
http://www.reefs.org/hhfaq/pages/picture_pages/faq_halimeda.html
http://www.reefs.org/hhfaq/pages/picture_pages/faq_caulerpa.html
http://www.reefs.org/hhfaq/pages/picture_pages/faq_feather_caulerpa.html
http://www.ffexpress.com/inverts/misc/racemosa.jpg
Note: these were all taken from reefs.org's very own hitchhikers FAQ
http://www.reefs.org/hhfaq/pages/picture_pages/faq_sargassum.html
http://www.reefs.org/hhfaq/pages/picture_pages/faq_halimeda.html
http://www.reefs.org/hhfaq/pages/picture_pages/faq_caulerpa.html
http://www.reefs.org/hhfaq/pages/picture_pages/faq_feather_caulerpa.html
http://www.ffexpress.com/inverts/misc/racemosa.jpg
Note: these were all taken from reefs.org's very own hitchhikers FAQ