star trek deep space nine(very good, esp series 4 onwards)
farscape(brilliant)
star trek voyager(quite good)
falling skies(not brilliant but worth a mention if nothing to watch)
BSG(never really watched it)
babylon 5(very good for its time)
firefly(brilliant)
terra nova(i thought this was good)
fringe(never watched it)
stargate, both SG1 and Atlantis(brilliant, both still 2 of my fav shows ever)
andromeda(i thought it was a bit cheesy but still good to watch if nothing else is on tv)
those are some i can suggest watching, also look at this link - its the top 100 sci fi shows(apparently)
but too short. if you want something with 2985629365927365 pages of story - SG1 + SG:Atlantis + SGU + SG: Continuum + SG: The Ark of Truth, total 17ish seasons, 2 movies, 20-22 episodes per season, way to kill all that free time!