• Greater Mark Of Desolation - Lovely rune for an AD top to start out, gives a little extra damage due to the penetration of the flat armour runes they will more than likely have.
• Greater Seal of Armor - Flat armour, helps with stopping early game damage as most top lane champs will be AD based, works out better to take these then the per level version.
• Greater Glyph of Scaling Magic Resist - As you probably wont be vs an AP champion at the start these work out great as they provide higher protection at a later level.
• Greater Quintessence of Attack Damage - This is for the last hits early on and to help possibly secure a champion kill early on
  
  
• Other Viable Runes:
• Greater Mark of Attack Damage - Can be used to give a fairly high damage early game to secure the last hits on kills though falls off a lot late game.
• Greater Quintessence of Attack Speed - Renekton's ulti deals damage to nearby targets, the bonus move speed really allows you to hug targets and stop any escapes.

• Cull the Meek - The reason for maxing this skill first is that its pretty much your top damage ability and the fact it gives you a way to steal life, keeping you alive a lot longer in lane.
  
• Slice and Dice - The reason why this comes second, well its your second higher damage ability early game and later on becomes your most powerful due to the scaling, its also your built in escape / engage and ranking it up lowers cooldown and increases the armour shred that comes with the second dash.
  
• Ruthless Predator - Maxing this last is pretty obvious to me as its the lowest damage by a long way, the stun duration is the same at all ranks and it applies on hit effects at all ranks.. so theres really no need to rank it till the end.
  
  
• Dominus - The Ulti, well this is ranked up at the ranks you can.

What They Do

• Reign of Anger - Your Passive causes you basic attacks and Q / W to build up fury, when you have over 50 your next ability will consume 50 fury and activate the "Empowered" version.
  
  
• Cull the Meek - This ability causes Renekton to spin his weapon around himself, it will deal damage to all enemies in a 225(approx) range which means it hits almost twice as far as a regular melee attack and will heal Renekton for 5%(20% vs champions) of the damage dealt. The "Empowered" version will deal 50% extra damage and doubles the amount healed
  
  
• Slice and Dice - This ability allows Renekton to dash for a range of 450 dealing damage to all enemies your pass through, if you do pass through enemies it allows a second dash that will deal damage to all enemies again. The "Empowered" version of the second dash will reduce champions armour by 15-35%(rank dependant)
  
  
• Ruthless Predator - This ability will will cause a green glow around Renekton and remain active for a while, while active his next hit (on creep or champions) will hit twice and stun the champion for 0.75 seconds, this ability will also apply any on hit effects. The "Empowered" version will hit 3 times and stun the target for 1.5 seconds
  
  
• Dominus - Renekton's ulti causes him to grow in size, gaining 300 - 600 bonus health (rank dependant) while active he will deal 40 - 100 magic damage to all enemies within a 175 range of himself (slightly greater than melee range) per second.