Help building my first (second) character!

[BowStreetRunner]

So... Once more, nothing else about which 4 feats should I pick?

Without high DEX you aren't going to be able to build an effective AoO tripper, so spiked chain and improved trip are probably out. (If you had high DEX then you would take Combat Reflexes, Combat Expertise, Improved Trip, and Exotic Weapon Proficiency: Spike Chain to set up an area of control around you where opponents would have a hard time moving.)

Spell Penetration (and Greater Spell Penetration) are heavily dependent on what your DM throws at you. If you run into creatures with high spell resistance, often you are going to wish you had both of these (for a total of +4). The rest of the time it's not going to matter much. An alternative is to avoid using spells directly on such opponents. Arcane Strike allows you to turn spells that would be useless against such opponents into a bonus on attack and damage against them. Or just look for spells on your list that have an entry of 'Spell Resistance: No'. I'd only take these if my DM used lots of these creatures and then I'd take both.

Taking a familiar is something I'd avoid until you've had a bit more experience with the game. I've found it tends to be a liability for many inexperienced players and often an overlooked and underutilized asset for most others. While there are players who know how to use familiars to devastating effect, I'm not one of them myself and won't go recommending it to you.

Of all the feats you are considering, I'd choose these: Arcane Strike is awesome on a Duskblade to begin with. Power Attack is good by itself and with Arcane Strike even better. Mobile Spell-casting is good and with your Arcane Channeling ability even better. Leap Attack on top of Power Attack, Arcane Strike, and Mobile Spell-casting can make for a truly lethal combination.

EDIT:

This is how your Duskblade can turn Leap Attack into leaping death. This assumes a build with Arcane Strike, Power Attack, Mobile Spellcasting, Leap Attack, 8 ranks in Jump, and 9 ranks in Concentration. You have STR 17 which gives +3 to attack and damage. You also have CON 14 which gives +2 to concentration checks. At level 6 you can cast 2nd level spells.

This is all going to occur on the surprise round, when you are restricted from taking a full round action but can still make a charge attack.

As you enter combat you are going to 'quick cast' the spell Jump to gain a +20 enhancement bonus on Jump checks for 6 minutes - long enough to last the entire combat.

With Mobile Spellcasting you make a DC 21 check to cast Shocking Grasp (5d6 electricity damage and +3 to attack if the opponent is wearing metal armor) AND move up to 30 ft AND arcane channel the shocking grasp at the same time. You need to roll a 10, so as long as you aren't in a threatened space you should be able to just 'take 10' and succeed automatically.

You are going to sacrifice a spell to Arcane Strike (1st level for +1 attack and +1d4 damage, or 2nd level for +2 attack and +2d4 damage). With Power Attack you can also subtract some of your attack bonus to raise your damage bonus by double that amount. If you are targeting an opponent in metal armor (+3 from Shocking Grasp) and sacrificing a 2nd level spell (+2) to Arcane Strike you will have a total +14 attack bonus with your STR and BAB, so even the max of -6 attack and +6 damage would still leave you with a +8 attack bonus. Pump up your damage by whatever amount feels comfortable to you right now depending on what you think you will need to overcome the opponent's AC.

With the Leap Attack feat you are going to combine a jump with a charge against your opponent. You currently have a Jump of +32 (9 ranks, 3 STR, +20 spell) so can standing long jump up to 15 feet without even factoring in your roll! Taking 10 that's a 20 foot standing long jump. You only need to cover at least 10 feat, so that's not a problem. Plus you ignore rough terrain in the squares you jump over. This doubles your normal bonus power attack damage and you are going to use a two handed sword so you will triple the extra damage from Power Attack.

So let's just say you are attacking an opponent in metal armor, take a -4 from power attack and sacrifice a 2nd level spell. Altogether you now have an attack bonus of +10 (+6 BAB, +3 STR, +2 Arcane Strike, +3 Shocking Grasp vs Metal Armor, -4 Power Attack), with a damage bonus of +27 (+3 STR, [+8 Power Attack x 3]= +24), +2d4, +5d6 electricity. That's 34-53 damage!