Steelix was moved down to UU and has only OU counters listed. Most of the basics are still the same, but there are a few things to note.
http://www.smogon.com/dp/pokemon/steelix
[Counters]
<p>Bulky Water types can switch into Steelix and hit with STAB Surfs. Blastoise can also Rapid Spin away any Stealth Rocks on the field.</p>
<p>Grass types can switch into Steelix with their Ground resistance and use Leech Seed or special Grass attacks. Claydol does not fear most varieties of Steelix and can proceed to hit it with Earth Power or spin away any rocks Steelix may have set up.</p>
<p>Probopass has the ability to trap Steelix with Magnet Pull, though it cannot switch into Earthquake. However, should it come in, it has the ability to Magnet Rise to stop Earthquakes and Taunt to prevent being Roared out. It can then kill Steelix using Earth Power.</p>
<p>Steelix will have trouble sponging most strong special attacks, but potential counters need to be wary of Steelix Exploding.</p>
http://www.smogon.com/dp/pokemon/steelix
[Counters]
<p>Bulky Water types can switch into Steelix and hit with STAB Surfs. Blastoise can also Rapid Spin away any Stealth Rocks on the field.</p>
<p>Grass types can switch into Steelix with their Ground resistance and use Leech Seed or special Grass attacks. Claydol does not fear most varieties of Steelix and can proceed to hit it with Earth Power or spin away any rocks Steelix may have set up.</p>
<p>Probopass has the ability to trap Steelix with Magnet Pull, though it cannot switch into Earthquake. However, should it come in, it has the ability to Magnet Rise to stop Earthquakes and Taunt to prevent being Roared out. It can then kill Steelix using Earth Power.</p>
<p>Steelix will have trouble sponging most strong special attacks, but potential counters need to be wary of Steelix Exploding.</p>