Could we detect an earth-like planet around another star? Could we detect an earth-like planet (e.g. similar distance from star, and similar size) with current planet finding techniques?  If an earth-like planet were orbiting our nearest star, excluding the sun :-), would we have detected it by now?  

It seems current techniques tend to find large planets orbiting close to their star, or for direct observation, find large planets further away from their star.  Likewise, we have found many very large planets very close to their star (e.g. hot Jupiters), and some rocky planets somewhat larger than earth close to stars, but not very many (if any) that are very similar to earth (e.g. distance from star and size).  It seems the current techniques available do not readily detect earth-like planets though, so it may be that there really are many earth-like planets, but we haven't seen them yet.  Here is an article on current planet detecting techniques.

http://en.wikipedia.org/wiki/Methods_of_detecting_exoplanets
The short answer is yes, the Kepler mission has used transits to detect nearly "Earthlike" planets, one of the classic examples is Kepler-22b is only about 2x the radius of Earth and has a year that is 290 (Earth) days. Kepler has detected many planets smaller than Earth and closer to the star. With more observing time Kepler could discover similarly sized or smaller planets at comparable orbits, so technologically transits can already detect  "Earthlike" planets. Practically, with Kepler's lost reaction wheel this has been difficult, but more Earth sized planet detections are likely from the K2 Kepler reboot.

Microlensing is more sensitive to planets further from stars, a next-generation space telescope like the WFIRST space telescope, which might launch in the 2020s, expects to be able to detect planets smaller than Earth at slightly larger distances from stars.

Taking a photograph or spectra, or directly imaging, a small planet far from its parent star is much more difficult, light from the Sun is around 10 billion times brighter than the sunlight the Earth reflects (a $10^{10}$ contrast), the sensitivity of current ground based instruments (like GPI) and the Hubble space telescope are closer to $10^7$.  WFIRST project will be be able to detect giant planets and may be able to detect Earthlike planets but the technology is not quite there yet.

Because of instrument stability and stellar variability, radial velocity instruments are not yet sensitive enough to pick out the incredibly small wobbles caused by a small planet in an Earthlike orbit. Future instruments, like the 100 Earths Project may get to this sensitivity in the moderately near future.