Eqium and Firium ($99 separately or $129 bundled), two debut products from Elemental Audio Systems, might provide all the EQ you'll ever need. Both plug-ins have extremely well-thought-out user interfaces that feature dual workspaces for easy A/B comparison, graphic as well as slider and button data entry, and multiple display formats to fit your work preferences. Both are currently for the Mac only (VST for OS 9, VST and Audio Unit for OS X), but additional formats are planned for the future. You can download demos and purchase the plug-ins at www.elementalaudio.com. While you're there, pick up the free sonic analyzer plug-in, Inspector, which displays a spectral analysis of your sound file and lets you set alarms to indicate when stereo-balance, clipping, and headroom limits have been exceeded.
Eqium (left) could easily become your workhorse multiband equalizer. It offers 11 filter types, including 2 high- and low-shelf curves, lowpass and highpass, notch, parametric, and 4- or 8-band harmonic filters. The harmonic filters can cut or boost a chosen frequency along with its first few overtones. You can insert as many filters of any type as you wish (within the limits of your CPU) to build as simple or complex an equalization spectrum as the situation requires. You can toggle individual filters in and out of a complex setup without losing their settings, and unused filters don't use any CPU cycles. Eqium comes in mono and stereo flavors. In the stereo version, any individual filter can have separate settings for the right and left channels. Setups can be saved to disk, and you can conveniently add a saved setup to an existing configuration.
You can think of Firium (below) as a 50-band graphic equalizer. It uses finite-impulse-response (FIR) filters, which have linear response and do not introduce phase distortion that can smear transients and blur stereo images. Firium is an ideal mastering EQ, allowing separate EQ curves for each stereo channel as well as several schemes for linking adjacent EQ bands when setting up the graphic. Other notable features include curve smoothing and scaling and an Undo history that lets you step back through previous EQ curves. Most importantly, Eqium and Firium both sound great and are surprisingly CPU efficient. For an example of Elemental Audio Systems' plug-ins in action, listen to the MP3 file eqfir.