To add to milepig's itinerary, I'd also suggest strolling along Wacker Drive from Michigan to Lake, and taking the "L" for these segments (day or night): Brown Line out to Armitage, Pink Line out to Damen, and Orange Line out to Halsted. Personally, my favorite angle on the skyline is from the west-northwest, rather than from the lakefront; since the skyline extends west and north from the loop, those just northwest get to be enveloped by city lights.

Some mid-range hotels with good river views: Hotel 71, Club Quarters on Wacker (not on Adams), and the Holiday Inn at Mart Centre -- which wins the award for "ugliest building with the best view." Some high-rise hotels a bit removed from downtown have good views on clear days, like the Hyatt Regency McCormick Place or Crowne Plaza Metro.

Rooftop bars have become a fad lately, and offer some really great views -- and you don't even have to buy a drink.