I've always liked Lost Soul's sneak attack feats (I think it was from a classless system he was trying to build by turning all class abilities to feats if I'm not mistaken)....
Here's some changes I've made on them:
Surprise Attack I [General, Regional]: You are the skilled at taking advantage of flatfooted opponents during an ambush.
Benefit: When wearing light armor or no armor, you can make a melee sneak attack at +1d6 damage against flatfooted foes during a surprise round.
Special: As sneak attacks aim for critical areas, creatures that are immune to critical hits are immune to sneak attack. Rangers can take this feat at level 1 and higher.
Prerequisites: DEX 13+, WIS 13+, Search +4, Spot +4, Proficient with light armors.
Surprise Attack II [General, Regional]: You are the skilled at taking advantage of flatfooted opponents.
Benefit: When wearing light armor or no armor, you can make melee sneak attacks at +2d6 damage against flatfooted foes.
Prerequisites: DEX 14+, WIS 14+, Search +6, Spot +6, Surprise Attack I.
Surprise Attack III [General, Regional]: You are the skilled at taking advantage of flatfooted opponents.
Benefit: When wearing light armor or no armor, you can make sneak attacks at +3d6 damage against flatfooted foes (within 30’).
Prerequisites: DEX 14+, WIS 14+, Search +8, Spot +8, Surprise Attack II.
Surprise Attack IV [General, Regional]: You are the skilled at delivering devastating attacks when opponents show weaknesses.
Benefit: When wearing light armor or no armor, you can make sneak attacks at +4d6 damage against flatfooted foes and foes that you are flanking.
Prerequisites: DEX 15+, WIS 15+, Search +10, Spot +10, Surprise Attack III.
Surprise Attack V [General, Regional]: You are the skilled at delivering devastating attacks when opponents show weaknesses.
Benefit: When wearing light armor or no armor, you can make sneak attacks at +5d6 damage against flatfooted foes and foes that you are flanking.
Prerequisites: DEX 15+, WIS 15+, Search +12, Spot +12, Surprise Attack IV.
Here's some changes I've made on them:
Surprise Attack I [General, Regional]: You are the skilled at taking advantage of flatfooted opponents during an ambush.
Benefit: When wearing light armor or no armor, you can make a melee sneak attack at +1d6 damage against flatfooted foes during a surprise round.
Special: As sneak attacks aim for critical areas, creatures that are immune to critical hits are immune to sneak attack. Rangers can take this feat at level 1 and higher.
Prerequisites: DEX 13+, WIS 13+, Search +4, Spot +4, Proficient with light armors.
Surprise Attack II [General, Regional]: You are the skilled at taking advantage of flatfooted opponents.
Benefit: When wearing light armor or no armor, you can make melee sneak attacks at +2d6 damage against flatfooted foes.
Prerequisites: DEX 14+, WIS 14+, Search +6, Spot +6, Surprise Attack I.
Surprise Attack III [General, Regional]: You are the skilled at taking advantage of flatfooted opponents.
Benefit: When wearing light armor or no armor, you can make sneak attacks at +3d6 damage against flatfooted foes (within 30’).
Prerequisites: DEX 14+, WIS 14+, Search +8, Spot +8, Surprise Attack II.
Surprise Attack IV [General, Regional]: You are the skilled at delivering devastating attacks when opponents show weaknesses.
Benefit: When wearing light armor or no armor, you can make sneak attacks at +4d6 damage against flatfooted foes and foes that you are flanking.
Prerequisites: DEX 15+, WIS 15+, Search +10, Spot +10, Surprise Attack III.
Surprise Attack V [General, Regional]: You are the skilled at delivering devastating attacks when opponents show weaknesses.
Benefit: When wearing light armor or no armor, you can make sneak attacks at +5d6 damage against flatfooted foes and foes that you are flanking.
Prerequisites: DEX 15+, WIS 15+, Search +12, Spot +12, Surprise Attack IV.