The Blaster is the standard sidearm of Colonial warriors. They are energy based weapons.
Blaster is the generic term for the hand held weapons seen on "Battlestar Galactica", also called laser Blasters. As lasers require a complex set of reflective mirrors, focusing lenses and an extremely powerful energy source to be effective, it is unlikely the weapons seen in "Battlestar Galactica" were true lasers.
Along this line of thinking, Blasters probably fired bursts of charged plasma. This plasma is produced by a laser beam inside the weapon, which is used to ionize simple compounds such as helium or argon into a plasma state. These compounds would be relatively abundant and easy to ionize with little energy, and as such the Blaster would not need to be a contained fusion reactor. Judging by the effects seen concerning Blasters in "Battlestar Galactica", this supposition holds true, as a laser gun would create a thin cutting beam, not an energetic explosion like Colonial/Cylon Blasters.
As far as how powerful these weapons are, from what was seen, it looks as if the Colonial Blaster can vaporize approximately 25cm^3 of metal, judging from when characters blasted walls and control panels. If the target destroyed is equalivant to iron, with a boiling point of 3,000° C, a Colonial Blaster would have a power output of approximately 315 kilowatts. Given the armor on a Cylon troop and the gun's ability to burn through flesh, this figure seems to more than hold true to what was seen in the series. Cylon Blaster Rifles were able to vaporize a similar mass as the Colonial hand gun, and probably had an output of roughly 1.5 megawatts. 
Colonial military laser pistols contain readouts that can indicate whether or not they has been recently fired. In addition, the energy signature in each weapon is unique, allowing tests to be conducted to prove if a particular pistol was used in a given instance (Murder on the Rising Star).
Behind the ScenesEdit
At the beginning of the series, the laser volley emitted from the pistol is invisible to the eye, with the exception of the accompanying flash from the muzzle. Later during the series run, particularly in Take the Celestra and The Man with Nine Lives, the laser blasts become red bolts due to the fact that Universal Hartland became the SFX factory for the Original Series .
The Blaster could be considered the Colonial equivilant of the UFP's 23rd Century Federation Type 2 Phaser.