OK I finally signed up to twitter and so far i'm following 8 sites.

Emily of course
NASA SDO (Solar dynamics observatory)
NASA
spaceflightnow
newhorizons2015
LRO NASA
MESSENGER 2011
CassiniSaturn


Any other suggestions?

Phoenix

Others I follow:

ulalaunch
NGLLC09
chrislintott
ProfBrianCox
DrLucyRogers
AlanStern
astro0_umsf
lorddrayson
therealBuzz
HiCommander
marssciencegrad
SPOTScott
dr_david_w
Nancy_A
martiansoil
jetlab
aggieastronaut
marschronicler
Astro_Mike
EuroSpaceAgency
BLOODHOUND_SSC (ok - not space - but it's rocket powered )
Gyeehill
nivnac
mars_stu
HiRISE
milesobrien
MarsScienceLab
MarsRovers
marsroverdriver

ESA Herschell
Hubble
Kepler

thanks