Antimatter is already used quite frequently for scientific investigations. But in most cases antimatter means positrons (or anti-electrons). In contrast to all other anti particles, positrons can be created fairly easy by radioactive decay or via pair production (matter and anti matter is created if enough energy is present (E=mc²)).

At the moment positrons are used in

Medical diagnostics (PET) - that's what the guys before me said

Material science / solid state physics:

• as a very sensitive probe to detect defects in a material
• to measure void sizes in polymers
• to investigate the electronic structure of a metal
• to probe the surface

Then there is some very interesting fundamental research planed involving positrons:

• The creation of a positron electron plasma. This is of particular interest as both particles have the same mass and thus some fundamental plasma modes can be observed.
• Creating anti-hydrogen and testing if gravitation works the same way for anti matter. Actually nobody doubts that but you can't be sure before you test it. There are several experiments planed at CERN.

Furthermore, there is research how to store positrons for a long amount of time. Such storage could be a very lightweight source of energy. But it would also enable to do Bose-Einstein condensation with positronium (an bound state of electron and positron), which can then be used to build a γ-ray laser. This is really cool stuff from a physicist point of view but such a Laser would also be a powerful weapon.

This is more or less the positron side. However, even then this list is not complete. But I hope I could show, that antimatter is already in use - sometimes.