The phaser rifle in all of its incarnations is a good bat and a parrying weapon. A bayonet might be useful, though. Even on the "pistol" sidearms...
Real-world pistol-knife combinations fail because pistols are difficult to balance to start with, having recoil and gas exhaust (meaning the presence of the knife blade harms the use as a pistol) and knives require some basics of holding ergonomics (meaning the pistol grip harms the use as a knife). TNG phasers would be a different matter: there's no reason to assume a bayonet would make the beam go awry, and the grip is oriented so that a bayonet aligned along the direction of the beam would actually be pretty ergonomic.
What I'd really like to see on the TNG phaser is a "stiletto rapier" functionality. It should be trivial for the handle to sprout a blade of adjustable length, from a few centimeters (for simple cutting purposes) to a dozen centimeters (knifefights) to a meter or so (slashing at an opponent armed with a typical edged or blunt instrument).
The STIX stiletto-katana is not the only way to go. The blade could be made of solid matter (say, simple steel rolling out from a spool), but also of some sort of jam-proof forcefields, or then materialized in place with replicator technology. Not all tech can be jammed, and making some of it jam-proof might actually result in a more reliable device than one based purely on mechanics. Larry Niven's variable-sword is always an option, too.
Timo Saloniemi