I have just installed NextGen Gallery plugin for my wordpress. Look no further if you want a very nice and clean gallery interface for your wordpress. You can download it here. A running NextGen Gallery can be found in my Gallery page.
After the installations, insert the followings code in your post or page to display your picture accordingly.
For a slideshow : [slideshow=id,width,height]
Example : http://nextgen.boelinger.com/slideshow/
For a album : [album=id,extend] or [album=id,compact]
Example : http://nextgen.boelinger.com/album/
For a gallery :
Example : http://nextgen.boelinger.com/gallery-page/
For a single picture : [singlepic=id,width,height,mode,float]
Example : http://nextgen.boelinger.com/singlepic/
For a image browser : [imagebrowser=id]
Example : http://nextgen.boelinger.com/2007/06/16/new-tag-picture-browser/
Read as startup : http://hqcode.com/?page_id=54
A further FAQ you can found here :http://alexrabe.boelinger.com/wordpress-plugins/nextgen-gallery/faq/
To integrate a widget into your theme manually, use the follow code in your theme:
For slide show:
<?php
if (function_exists(’nggSlideshowWidget’))
{ nggSlideshowWidget($galleryID,$Width,$Height); }
?>
For random images :
<?php
if (function_exists(nggDisplayRandomImages))
{ nggDisplayRandomImages($number_of_pic,$Width,$Height); }
?>
For recent images :
<?php
if (function_exists(’nggDisplayRecentImages’))
{ nggDisplayRecentImages($number_of_pic,$Width,$Height); }
?>
Source: http://wordpress.org/extend/plugins/nextgen-gallery/

Hi there, thank you for this useful info on NextGen Gallery. Do you know what code I would use to embed Image Browser as a widget in my theme?
Thank you so much for your time.