I agree with Whitestrat.
Sustain stems from the guitar. There are many factors that affects the sustain;
Common things that you already know like, the inherent acoustical quality of the guitar, how well the neck fits, the bridge and saddles, the trem-block, if the 'speaking' points of the strings have good contact with the bridge and nut, etc.
Talking about the nut, itty bitty stuff like that matters too.
For example, what material the nut is; plastic generally don't give a clean sound.
Also, how well-cut the nut is, how deep your strings are sitting on the nut.
Too deep and there's a 'pinching' effect, that equates to a definite loss of sustain. However, too high up and the strings might pop out when you bend them. Especially the B-string when I bend the high-E.
Other small stuff like the height of the pickups also plays a part.
For example, if you have individual adjustable pole-pieces of your pickups, and you bend a lot, you can try having the pole-piece screws higher under the middle strings and lower under the outer strings so that they will follow the arch of the string heights. This may cost you some unevenness of output, but it will allow the strings to sustain much better when bent.
And then for single-coils, especially those on Strats, the magnets are pretty strong and will pull on the strings. If you have very little clearance between pickups and strings, it'll probably induce some distortion. While this might sound desirable, this will also cause a distinct loss of sustain. The magnetic attraction between string and the pickup's magnet is the culprit, causing this 'dampening' effect' as when the pickups tries to attract the string it will kill its vibrations.
So, the secret to awesome sustain is not some magic pedal. You're better off with acquiring at least a decent quality guitar that is well-setup and well-configured.
