If you're talking soft caps, those are long gone. The only thing that I know has a hard cap are light/heavy attack damage modified by weapon/spell damage, sprinting speed, and critical damage percentage. Most everything else is without limit within the boundaries of gear, abilities, and passives can provide. Depending whether you're talking PvE roughly 32,500 resistance for 50% damage reduction cap and 18,200 Penetration; whereas PvP there is no limit.
PvE
Armor Cap: 33K (50%)
Max Monster Armor / Penetration Needed: 18.2K (Tanks in organised groups may provide most of that, e.g. 14K to 16K)
Speed Cap: 200% (100% over normal non-sprint running speed)
Health / Mag / Stam: No cap, but generally not efficient to stack
Weapon / Spell Damage: No cap, tends to be more efficient to stack than mag / stam (better multipliers)
Crit %: 100% (very hard to reach without sacrifice, other than by using Acuity, thus effectively no cap)
Crit Damage Cap: 125% (75% above your default 50% bonus)
Block mitigation: Possibly 91% (based on my own experiments)
PvP
Armor Cap: The penetration of your attacker + 33K. Sky is the limit. In practical terms 45K as a troll tank, but not if you want to do damage.
Max Penetration Needed: As much as possible, but it's all a tradeoff. At some point (20K) you're probably better off worrying about crit or self-healing (more weapon / spell damage / crit % / crit damage). Really the only way most people get to 20K+ is with Balorgh, Corrosive Armor, or Onslaught.
Health: No cap. You can make do with 25K, less as a ganker. 30K is preferred as a Brawler.
Crit Damage Cap: 125% + the target's crit resistance. This is usually more than you can realistically achieve. Can't have enough on certain builds such as NB, due to guaranteed crit from stealth, or a Mechanical Acuity build. Not the be all / end all, but a viable way of building.
Crit Resistance: No cap that I'm aware of, but a compromise to stack other than with Rallying Cry.
PC EU: Magblade (PvP main), DK (PvE Tank), Sorc (PvP and PvE), Magden (PvE Healer), Magplar (PvP and PvE DD), Arcanist (PvE DD)
PC NA: Magblade (PvP and PvE every role)