Vortilons and Vortex Generators
To clarify, since there seems to be an element of confusion with the terminology.
A vortilon is precisely as described by PickyPerkins, and are fitted to the Hawker 800 as he notes, and also to the Bombardier Conti...oops Challenger 300. It is a flat plate surface mounted under the leading edge of the wing, and generally looks like it is intended to spear any birds or groundcrew near the L/E. It is a device for control of the wing flow (usually concentrating on stall) by means of a generated vortex.
A vortex generator is a more general term, but is normally meant to be a small device, typically triangular-ish, often placed in a group, which is used to either re-energise the local flow and prevent separation or used to "fix" a shock on a transonic aerofoil and prevent unwelcome effects due to the shock migrating.
A wing fence is a flat plate device, typically (but not always) wrapped around the leading edge and extending chordwise along some or all of the wing. It is used to either prevent (minimise) the effect of spanwise flow and/or to control the originating point and development of a stall.
And a winglet, which seems to have got caught up in this discussion, is a device on the wing tip which converts some of the "wasted" energy in the tip vortex into thrust, and gives the benefit usually asociated with a larger span. Some very advanced and specialised wing tip devices can almost eliminate the vortex, with attendent improvements to range, fuel burn, etc.