For a speed 600 you will want a 25 amp ESC. Depending on what battery and prop you are going to ue you might be able to use smaller but 25 should be adequate.

$35
http://www2.towerhobbies.com/cgi-bin...&I=LXKBF4&P=ML

$18 This is the ESC for the Spectra. Uses the same motor
http://www2.towerhobbies.com/cgi-bin...?&I=LXBNC5&P=7

If you are using 6 to 8 cells you will be fine. If you are using LIPO pack you will want an ESC that has a LVC that can be set for lipos. The first one can be set for Nixx or Lipo packs.

There are a number of GWS ESC on this page. Some for NiXX and some for Lipo use.
http://www2.towerhobbies.com/cgi-bin...S2=ESC&S3=&S4=