Here is a Rogue 19\Bard 17\Blackguard 4. He has 4 attacks with his kukri, pretty good buffing spells and a song from Bard levels, Divine Shield\Might which allows to use his charisma bonus for ac and damage, 11d6 Sneak Attack (or more if you choose Improved Sneak Attack), good saving throws because of the Dark Blessing.
Race: Halfling Alignment: Neutral or Chaotic Evil Stats(at the character creation): STR 12 DEX 18 CON 14 WIS 8 INT 10 Cha 14
Level and feat progression: 1-Rogue(1)-Tougness 2-Bard(1) 3-Bard(2)-Weapon Finesse 4-Bard(3)-> +1 STR 5-Bard(4) 6-Bard(5)-Power Attack 7-Rogue(2) 8-Rogue(3) -> +1CHA 9-Rogue(4)-Cleve [Remember to have at least 5 Hide on this level] 10-Blackguard(1) 11-Blackguard(2) 12-Rogue(5)-Exotic Weapons -> +1 Cha 13-Rogue(6) 14-Rogue(7) 15-Blackguard(3) Divine Might 16-Bard(6) -> +1 DEX 17-Bard(7) 18-Blackguard(4)-Divine Shield 19-Bard(8) 20-Rogue(8) -> +1 DEX 21-Rogue(9)-Improved Critical: Kukri 22-Rogue(10)-Improved Evasion 23-Rogue(11) 24-Bard(9)-Curse Song -> +1 DEX 25-Bard(10) 26-Bard(11) 27-Bard(12)-Great Dexterity 1 28-Rogue(12)-> +1 DEX 29-Rogue(13)-Deffensive Roll 30-Rogue(14)- Great Dexterity 2 31-Rogue(15) 32-Rogue(16)-Epic Dodge ->+1 DEX [Remember to have Tumble maximized by this level] 33-Bard(17)-Great Charisma 1 34-Bard(13) 35-Bard(14) 36-Rogue(18)-Great Charisma 2 -> +1 CHA 37-Rogue(19)-Crippling Strike 38-Bard(15)- Epic Skill Focus (Discipline) or Improved Sneak Attack or something for the bard song, any feat 39-Bard(16) 40-Bard(17) -> +1 CHA
Skills to maximize - Perform, Tumble, Use Magic Device, Discipline. Other skills, worth to be kept high: Hide, Move Silently, Listen, Taunt, Concentration, Spellcraft. Unfortunately, the character doesn't have skill points for everything, so you'll have to choose.