It's well worth checking out the entire Topaz range of plugins except, perhaps, photoFXlab which is a standalone host program for using the other plugins without the need for Photoshop.
Adjust is a general-purpose plugin for editing the 'look' of a photo. Detail is for adding small, medium, and large local contrast and so is good for sharpening and adding or removing clarity and structure. Simplify and Clean do the opposite and are great for getting the 'painterly' look. Remask is great for masking hair, trees, bride's veils, etc. B&W Effects is similar to Nik's Silver Efex, ie creating monochrome photos. Lens Effects is good for changing the focus of a picture to some degree by using depth maps, and can mimic the look of a fair number of lenses; it's also great for adding mist and fog to your photo, adding filters, and other effects. DeNoise does what it says in the name. Infocus goes some way toward rescuing out-of-focus photos. Star Effects is for adding stars, lens flares, and other lighting effects. Finally, DeJPEG can be used for removing JPEG compression artefacts of various kinds.
I also use OnOne Software's Perfect Effects which is great for doing global and local adjustments in a similar way to Topaz Adjust and also comes with a big stack of presets. It can be used as a plugin to PS, Elements, Lightroom, Aperture, and as a standalone program. OnOne have other plugins that rival Topaz and Nik Software, such as Perfect Mask and FocalPoint. They also offer Perfect Portrait, Perfect Black and White, Perfect Layers, and Perfect Resize.
With Nik's Viveza you can get a photo ready for print or upload quicker than most other methods, using something called U-Points. Nik also offer Color Efex Pro which is like Perfect Effects but with fewer presets and less control (IMO). They also offer HDR Efex for producing HDR photos.