Cyber is a freeware 'simple sample player'. There are a few of these about now, such as Helios and 3S, but Cyber is definitely my pick of the bunch at this point, in part because it will pick up pre-existing loop points as it loads samples.
If you have such samples (e.g. from a sample CD like the one from Maz) then a couple of right-clicks in Cyber gets you instantly to the lead or pad sound you need. Alternatively, you can prepare your own samples using the precision looping and crossfade tools in Soundforge or Wavelab.
The likes of Halion and VirtualSampler can do this of course - but they cost $$ and (in my opinion) clutter up the screen with all their options. Cyber is very much more stripped-down, but has exactly the key features you want: velocity-sensitive, a resonant filter, separate envelopes for volume and filter, midi control of cutoff and Q... and it sounds GOOD!
Support is great too - I emailed a query about looping and within a couple of days a new version was released with the feature I had asked for - too kool. It originates as a plugin for Massiva but is working flawlessly for me in Cubase. No manual really necessary, but there are some helpful comments on the Cyber webpage if required.
Overall, this is a highly recommended little tool if you're already close to maxing out you CPU with VSTi synths and need to slip a few sample-based sounds into the mix with minimum fuss and bother!
(BTW - the KvR ratings system really needs a "not relevant" option...that's what I would have liked to have given for Presets)