wp-hashcash, which is recently updated has been my favourite spam plugin, well probably of any plugin, so far. I tried SpamKarma and Spaminator, and I saw all the for and against for each plugin. Hashcash (previously stopgap) is such a simple and devious little plugin.
Upload the js file, upload the php file, run the plugin and that's it. no configuration, no messing around - it has never moderated any author comments, it has never moderated legtimiate comments and it has stop ANY spam from appearing. Of course I don't use robots.txt and my meta info in my header is not up to date, but before this plugin and with either of the other two plugins I still recevied and managed spam comments on a regular basis.
Iimage Gallery based on the Image Gallery (?) plugin by a French WP users I believe, this has done a lot with regards to improving on the base. It allows creation of thumbnails, resampling as well as resizing, includes a mutltiude of options on how to link an image, either as a thumbnail, as a full image and so on.
It allows a lot of control within the pop up window, including uploading and deleting from within the pop up. It's improving with each build although since the quicktag button was introduced there have been issues with it not working as it should, it seems like a bug where the some have it working and others don't. still I've very happy with the 1.41 version of the plugin.
simple php gallery - even after I dumped it once, and althougt not strictly a plugin it is a brilliant WP addition. It may not have a lot of options, but if you just want images uploaded to a folder, want auto-thumbnails and a gallery that is frankly astongishingly easy to integrate not only into WP but also to make it look like the rest of your site then no other gallery "plugin" comes close to simple php gallery IMHO. If this had a few more features, and an administrative backend, it would be pretty perfect.
comment quicktags - if there is one way to include and style the quicktag buttons for use in the comments page, then this is it. upload, activate and style. simple, but oh so useful.
custom posts per page/custom query string a clever little plugin that allows you to manage posts depending on the page so you can set it to display 6 posts archives, 10 posts in a category, 2 posts if it's home, and so on. Simple and easy to manage with it's own interface within the admin panel.
category images - another c2c plugin and one that offers a multitude of options over the existing tag within wp I feel. It's a brilliant plugin and piece of cake to use, I use for both sites I'm working on and the options available just add to the fun of this plugin. Both plugins do essentially the same thing, with some minor difference, it's down to preference and need I suppose.
customisable post plugin again from c2c the flexible nature of this plugin and the updates it has gone through, as well as the upcoming and tasty prosecpt of upgrades in the waiting, have made this plugin invaluable for my needs. it's options, and it's ease of use as well as the huge number of variables allow the mix and matching of different ways to display posts in different containers. it's just brilliant.