I typically regard facing Riven as a free lane unless I get camped (which is why I spam wards). She's not hard to beat as a lot of top laners if you are smart enough to adjust your build path and play-style appropriately.
If I'm playing an AD bruiser (i.e. Garen, Renekton, Darius, Olaf), I'll often grab a couple Doran's Blades before building into Sunfire Cape or Phage. You have to much health/armor for her to burst down immediately, a good amount of sustain, and comparable damage in trades (assuming you don't let her jump on you and immediately retreat).
If I'm playing a Trinity Force champion (i.e. Jax, Irelia), I'll typically prioritize 2x Doran's Blades, Phage, and Ninja Tabi. This combination provides a lot of health, AD, armor, lifesteal, and mobility which can let you deal with Riven and it doesn't really set you back in your build.
If you are playing a CDR/mana-reliant champion (i.e. Maokai, Malphite, Cho'gath, Nasus), rushing Frozen Heart can prevent her from killing you while allowing you to use your abilities freely in lane.
If you are playing an AP champion, Seeker's Armguard is a fantastic early purchase.
If you want to make Riven hate herself, you can just pick Taric and rush Iceborn Gauntlet against her. You out-sustain her, you are to durable to burst down, you make your entire team more durable against her, you have a targeted stun to stop her, and you can outdamage her in a straight-up fight.
The biggest reason I've seen Riven snowball is because her opponents refuse to adjust their playstyle: a Jax will rush Trinity Force without purchasing any health or armor, a Vladimir will rush Hextech Revolver instead of Seekers Armguard, or a Maokai will rush Rod of Ages, etc.
The other big reason is that many players are impatient and greedy. They'll over-extend in lane to get CS instead of waiting for it to come to them, they'll clear waves instead of freezing the wave near their side of the map, they'll try to get CS instead of farming the jungle or roaming if the Riven is freezing and zoning them, etc.
Anyways, if you find someone ballsy enough to first pick Riven, make them regret their choices in life.

Also, it can help to set up a heavy armor rune page to deal with AD assassins/fighters who rely on early snowballing.
Quints: Flat Armor
Marks: AD or Hybrid Pen
Seals: Flat or Scaling Armor
Glyphs: Flat MR or Scaling MR or Scaling CDR