Planet detection methods:
Radial Velocity (Doppler, wobble)
best at finding high mass close in planets. Will be able to find lower and lower mass planets in longer orbits.
Yields period, lower limit to mass. Limited by activity of star, and stars cooler than A-type.
Has found most planets. Many multi-planet systems.
Transit method
best at finding large (in size) and so high mass planets close in to star. Kepler is space mission, that will be able find Earth mass planets in Earth length orbits. Will find smaller size and longer orbit planets. Limited by stellar activity. Measures size (not mass) and orbital period of planet.
Has found lots of planets. Possible to detect exo-moons
Microlensing
Best at finding medium to large mass planets beyond the snow line. Found 17 planets. Limited by seeing quality, and telescope time. With space mission would be able to find sub Earth mass planets.
Direct Imaging
best at finding large, high mass planets far from their host star. Also good at finding young therefore hot planets far from star. Currently limited by technology. Possible major limit is brightness of exo zodiacal light. Several planets found, including first direct spectrum. Team up with spectroscopy and spectropolarimetry to characterize surfaces/atmospheres of planets.
Astrometry
Best at high mass planets far from planet. No firm detections (VB 10 withdrawn). Will require space mission. Limited by technology, and stellar activity.
Timing
Best at finding short period planets. Needs stable clock (pulsar, pulsating white dwarf, short period pulsator) for host star. Has found several planets including lowest mass planets (moon mass).
Radio
Possible to detect the magnetospheres of planets (most likely giants) with low frequency observations. Maybe find a few with LOFAR. Of course there is always a possible detection of a intelligent signal (also in optical).
Serendipity
Finding evidence of super high tech civilization. Dyson spheres etc