In few case I use these plugins to help :
- Thumbnail on Excerpts, some themes didn’t have thumbnail codes in excerpts whereas mostly magazine style themes looking better with a thumbnail in homepage. This plugin will add the first image at that post to appear as thumbnail, we can resize to match excerpt height and width without painly coded on templates.
- Get The Image, similar with plugin above, this plugin can grab an image by custom field input, post attachment, or extracting it from the post’s content but if the template have thumbnail code.
- Autothumb, In case the theme really hard to hack for showing thumbnail, I use this plugin which integrates phpThumb into WordPress.
- My Category Order Plugin, help to rearrange category navigation, with drag and drop tabs only, in case we need last added category put in first navigation bar.
- Google Analytics Plugin, although I’m fans of Google Analytics and prefer using Awstat only but sometimes buyer need to see Google stats, so I use Ultimate GA which is more flexible because no need manually add analytics code when we change the theme.
- Twitter Plugins which I usually use is WP-Followme and Tweetmeme for Retweet feature.
- Featured Content Gallery Plugin is the simple and easy thing to add slider featured post/images at homepage.
- Featured Posts at Widgets sometime needed to show specific category which want to show as headline at homepage, I use Featured Post With Thumbnail or Factory-Featured (I must codded this first).
- Tubepress Plugin to showing Youtube video gallery within grids.
Well, Essential Plugins and those plugins above that’s all my significant mates 
