For mastering I either remain in protools, or transfer to a 2 track Studer, whatever the program requires.
There are a whole bunch of tools to use, but it all really depends on what the to be mastered material needs.
As we're talking plug-ins, my absolute favorite is
the TC MasterX 5 band, which features integrated multiband expansion, compression and limiting, especially for mastering applications.
Here are some of the features: (stolen from the TC website):
• 5 and 3 Band Expander/Compressor/Limiter (5 Band: Mac only)
• Gain Control per Band (+12 – -25 dB)
• Adjustable Band Crossovers
• Gain Reduction Meter per Band
• Consecutive clippings counter
• Limiter/Expander Indicator per Band
• Dynamics Processing Curve Display per Band
• Hi Precision ppm meters with selectable hold modes
• Target Control per Band, for module specific frequency adjustment (hi/lo)
• Look Ahead Delay of up to 10 ms
• Digital Ceiling with accuracy of up to 0.01 dB
• Separate L/R Input Level controls for post-balancing mixes
• Soft Clipping for Limiter stage (analog emulation)
• Dithering: 22, 20, 18, 16 and 8 Bit (Uncorrelated)
Takes quite a bit of practice to use it properly and effectively, but once you get accustomed to it, its awsome.
I have also tried MasterTools form Apogee, but went back to the TC.
The next "can't do without" TDM plug-in is a totally essential tool -
SpectraFoo Complete.
Foo complete features just about every measuring tool available, all extremely accurate. Get the Foo stuff in hardware, and your wallet will be over 60.000 bucks lighter!. From screen size VU's, peak meters, Lissajous phase scopes, oscilloscopes, code matric meters, signal generators, correlation meters, you name it, its got it.
Next, I think the best sounding EQ, If anything needs something this is the first one I'll try - the TC EQSat. # band parametric and 2 band shelving. On top of that, it has one of the best sounding "soft saturation" algorythms. (tape similation)
Those are the ones I use most
Other TDM plug-ins I like using in mastering (again - it all depends!!) are:
Cuan's Wide.R, if a mix is lacking in stereo image and could really use some "pulling apart"