Anything comment related: Just get Disqus. It does pretty much everything you need (including tweets) and it’s cleaner and less confusing than the mess of brambles that is the WordPress comment system.

The More Fields plugin is killer. I use it on my site and it allows me to do some pretty complex stuff with my site’s design. I would not be able to make my site work without it.

And I’m a big fan of both Apture itself and the plugin that makes it a cinch to add Apture to your site. It’s incredibly useful.