Tactical raging
At higher levels, and even at low-mid levels with the Extra Rage feat and other options, a standard Barbarian has more than enough rages to enter one in every encounter during the day. The only penalties are the loss of skills that the Barbarian wasn't investing in anyways and a minor AC penalty that matters less and less as attack bonuses become greater and alternative attack forms that don't target AC (or attack touch AC) become more common. So why not rage all the time?
Under this variant, rages have unlimited uses. Not per day, not per encounter, just at will, with a few exceptions. Instead, the Barbarian gets a number of different rage variations, each of which have certain limitations, situations in which the Barbarian can be forcibly removed from his or her raging state.
Once your rage ends, you become fatigued for some time. You cannot enter a rage again until after that duration has elapsed, even if you are immune to fatigue or the condition is removed prematurely.
A Barbarian knows one type of rage at level 1 and gains a new type known every 4th level. The Extra Rage feat grants knowledge of 2 new types of rage. Anything else that gives an extra rage per day instead gives an equal number of rages known.
Rage still lasts for up to 3 + Con mod rounds, unless you are knocked out of it early. I'm not addressing, yet, what happens as rage improves at higher levels (greater/mighty rage and indomitable will).
Skill restrictions refers to the standard limitations on what skills you can use in a rage. Not all types of rage retain them.
Battle Rage
Restrictions: None.
Effects: +4 Str, +4 Con, +2 Will saves, -2 AC, skill restrictions.
Limitation: Rage ends if you do not attack an opponent nor are attacked by an opponent for 1 round.
Aftereffects: When your rage ends, you are fatigued for 2 rounds.
Berserker Strength
Restrictions: You cannot call upon your Berserker Strength while you have more than half your maximum hit points.
Effects: +4 Str, +2 Will saves, DR 2/-, fast healing 1, skill restrictions.
Limitation: Rage ends if your hit points rise to greater than half your maximum.
Aftereffects: When your rage ends, you are fatigued for 5 rounds.
Deathless Frenzy
Restrictions: You cannot enter a Deathless Frenzy while you have more than one quarter your maximum hit points.
Effects: +8 Str, +2 Will saves, -2 AC, extra attack on full attack (all at -2), skill restrictions. You are not disabled/dying from hp or 0 or less, nor are you staggered/unconscious from nonlethal damage equal to or greater than your hp. Add 1/4 your maximum hit points to your actual hit points to determine whether or not you are dead.
Limitation: Rage ends if your hit points rise to greater than half your maximum.
Aftereffects: When your rage ends, you are fatigued for 5 rounds and exhausted for 2 rounds.
Duelist's Frenzy
Restrictions: You cannot enter a Duelist's Frenzy while flanked.
Effects: +2 Str, +2 Dex, +2 Con, +1 Will saves. Choose a single opponent you are aware of when you enter the rage. You deal +1d4 damage on all melee attacks against that opponent.
Limitation: Rage ends if you are attacked by a flanking opponent other than your chosen opponent.
Aftereffects: When your rage ends, you are fatigued for 2 rounds.
Furious Bulwark
Restrictions: None.
Effects: +4 Con, +2 Will saves, DR 5/-.
Limitation: Rage ends if you move more than 5 feet during any round.
Aftereffects: When your rage ends, you are fatigued for 2 rounds.
Short Fuse
Restrictions: None.
Effects: +2 Str, +2 Con, +1 Will saves, -2 AC, skill restrictions.
Limitation: Rage ends after 3 rounds, regardless of the remaining duration.
Aftereffects: When your rage ends, you are fatigued for 2 rounds.
Superstitious Rage
Restrictions: You cannot enter a Superstitious Rage while subject to fear (shaken, frightened, panicked, or cowering).
Effects: +4 Str, +2 on saves vs. spells and supernatural abilities, -2 AC, skill restrictions.
Limitation: Rage ends when you fail a save against or allow yourself to be willingly affected by a spell or supernatural ability, excluding those you use on yourself.
Aftereffects: When your rage ends, you are fatigued for 1 round. If your rage ended as a result of a spell or supernatural ability, you are also shaken for 3 rounds.
Whirling Frenzy
Restrictions: You cannot enter a Whirling Frenzy while prone, entangled, or immobilized.
Effects: +4 Str, +2 dodge to Ref saves, +2 dodge to AC, extra attack on full attack (all at -2), skill restrictions.
Limitation: Rage ends when you fall prone or fail to move at least 5 feet during your turn.
Aftereffects: When your rage ends, you are fatigued for 2 rounds.