Recently I have been experimenting with a Sightstone on Tops, Mids and Junglers. Of course it is a no brainer item for Supports and not needed on an ADC because the support is covering your lane, but a sightstone pays itself off in 15 minutes of ward coverage, assuming you are using both wards at all times. Not to mention the fact that it sells for 490G, 70% of the initial investment. The reason I see some supports be a bit unsure about the Sightstone is they can only have 2-3 wards down at a time, not enough to cover everything that needs to be covered. However if there are 4 people with a Sightstone, you could cover all 4 exits of the enemy jungle, both of your buffs or their buffs, depending on what is required, Dragon and Baron and even have one spare ward (assuming the support upgraded to a Ruby Sightstone) for checking a suspicious bush or whatever is needed.
I find that if 2+ people have a Sightstone and communicate properly the ward coverage at so little gold is extremely effective. Obviously the carries, top and possibly Jungler would need to sell their Sightstone for late game items once they finish their first 5 items, but at that point the Support could just sell their Ruby Sightstone for 70% of the initial investment and go back to 5 wards at a time anyway. What is everyone's thoughts of investing in multiple Sightstones for extreme ward coverage?