Just three? I mostly tend to watch series that are completed ie. Sopranos, Frasier and such, but from the ones still running, in no particular order:
House – Almost every episode is a delight and oftentimes Emmy-worthy. Hugh Laurie IS House. The supporting cast is also excellent with Robert Sean Leonard, Lisa Edelstein, Jennifer Morrison, Omar Epps and Jesse Spencer being more than just people for House to ridicule. Truly a great show.
Top Gear – With every new episode, even if it's a somewhat average one (and Top Gear average is like the best episode of any other show running), I sit through it with a huge smile upon my face. The dynamic of the three presenters is just awesome and you never quite know what to expect of the next season, so you're always kept guessing and thoroughly entertained.
South Park – Got the nudge over Family Guy as the latter is just goofy, South Park actually brings to attention some quite serious issues but never gets preachy or overly moralising. Matt Stone and Trey Parker keep creating genius with every episode.
Other shows I watch include the ever brilliant Dexter (still to catch up on 4th season though), Entourage (lost a bit of spark in the beginning of the season but finished up very strongly although I don't think there's too many seasons ahead, everyone seems to be doing their own thing now), Simpsons (the classic, but still going strong) and Aqua Teen Hunger Force (pure genius).