I like to develop a distinctive 'shound' and I find too many plug-ins distracting, I'm not too much of a fan of so-called analogue hardware 'emulations', there are some things that must have a gazillion emulations by different makers such as the LA-2A clones, and I fail to see the point of having more than one that operates in that intended ball-park. Saturation fx like tape sims baffle me too I think after you've found your own recipe for dirtying up your digital in a nice way then there seems little point in picking up all the variations on that theme that are out there.
If it's studio type FX then I probably have around 50 all told and that includes the Sonitus suite which gets a lot of use. Out of that many probably half get used regularly and the other half perform specialist type functions that only get used in specific circumstances. I don't own anything I don't have a use for.
This one is my current favourite and it gets used on about every project these days, I wish I could get a VST version, it's a shamelessly digital upward compressor, you basically run your audio through it first off to find the highest peak and set the curve to compress upwards so you can leave low level noise where it is and just squash from the lowest point in your good signal toward your highest peak. It's a fantastic vocal leveller among many other useful dynamics tasks.
http://shop.propellerheads.se/product/selig-leveler/ I love innovations like this rather than more of 'me too' boutique models from yesteryear I think it is high-time developers took more risks in producing useful tools like that rather than pandering to the plug-in collectors who seem to want every bit of old iron found in a studio of yore recreated in digitall form.
These people seem to be like model railway enthusiasts trying to create a diorama faithful to the golden age of steam to show off what they've got to their equally insular pals rather than having creative fun with sound.
Each to their own I suppose but I want plugs that bend sound into cool shapes I don't care what gear folk used in the '60's let alone wanting recreations of it.