DAS 660 is quite good, although it doesn't sound "transparent" to me, but then again, I use it mainly to get a "spikier" sound, and I'm certainly no engineer
Usually, I put the DAS SL9000 Master Compressor on the master bus to level the signal a little, even while mixing. This fills up the sound a lot, but it's useful to have a sense of the finished mix. When I want "transparency", I usually go for the DAS 2A, moderately set, and for trickier material, the DAS1610 or Wolf's Kompressor give you some more parameters to tweak and sound very good to me.
What I'm never happy with are multi-band compressors - I haven't heard a single one that I like. Usually, I use Ozone, but I remember Waves C4 (a compander) was kind of nice, although Waves stuff is quite expensive. The Optimaster is way too loud for me (yes, I know, tweak, tweak, tweak), and the orbitone stuff doesn't really click with me. Could use some guidance in this aspect, as I tend to avoid any sort of multiband compression, and try to get a balanced mix with the eqs and all... Only sometimes a friend brings me a song to "master" for CD, and I feel it could do with some multiband compression, but I don't have a satisfactory tool o work with....
What I have been enjoying, though, is a few select VSTs I have been trying out, like PSP's Vintage Warmer and MasterQ, and Voxengo's GlissEQ and Soniformer (a bit like SBC, but with far more bands). And I'd love to try PSP's Bob-Katz-endorsed Xenon as a loudness maximizer, but I'd have to buy an iLok first, so.... no. Same problem with Sonnox, Abbey Road, etc... But these are some serious VSTs, if that's your thing...