Haste usable by:

[boolean]

If you're looking at qualifying for Swiftblade, there are a couple of things to keep in mind.
1. The requirement for Swiftblade is "Special: Must have spent the entire previous level using all 3rd level spell slots to exclusively cast haste." So, technically, builds that get haste at a level higher than 3rd (like using the Celerity domain) won't work. Using a class that gets it at a lower level can work, you just need to use your 3rd level slots to cast it.

A lenient DM could simply change the requirement to "Must have spent the entire previous level using all spell slots of the appropriate level to exclusively cast haste."

2. Swiftblade levels advance arcane spellcasting, not divine. So, builds using Cleric with Time or Celerity domains don't work as well. Again, your DM could change the class to advance divine casting in this case.

 

[Krud]

I think a good gish build is still your best bet.
Maybe Barb1/ Battle Sorc 6/ Eldritch Knight X/
Mithral Breast Plate or Chain Shirt + Shield Spell = Good AC+ 40ft movement
Wield a greatsword for good power attack synergy
Buff yourself with Bullstrength, mirror image, expiditious retreat etc

You'll lose 2 Points of Bab over a straight Barb. Also theres less HP, but you'll have better will saves. The Hp you can prop up with bears endurance or false life anyway, and you can buff your AC through the roof. You'll be restricted in lvl2 spells by the battle sorceror variant, so you'll have to be choosy with those.

Only problem is rage stops you from casting which isn't exactly a good idea. Still Bullstrength +Rage+Power attack+Arcane Strike+Haste=lots of damage

Theres also that Barb variant, whirling frenzy or something from UA.

 

[Darklone]

I think a good XXX build is still your best bet.

Jehova, Jehova!

Where are my stones?

 

[escaflowne777]

Alright, so divine classes are out of the question, I'd rather not take just on level of any class unless I need fighter for a martial weapon proficiency. Paladin, I'm not quite sure how that would work... and trapsmith has haste at first which is impressive, but I need it in a third level spell slot. So other than wizard and sorcerer, what are my options? Swiftblade is such a specialized class, and has many amazing abilities, but it's so freakin hard to get into.

 

[Bagpuss]

War Priest from I think either Complete Warrior or Complete Divine gets to Haste folks. It's more a class ability than the spell added to his list.

 

[FreeXenon]

An elven battle Sorcerer gets you right in by 6th level. Elves get longsword as a free martial weapon as well as long bows.

If you take human you would have the extra feat to get a martial weapon and then go straight Battle Sorcerer.

Paladin has great synergy with Sorcerer due to the Charisma Requirements. Starting with Battle Sorcerer, a Paladin 1 or 2 /Battle Sorcerer 6 would be interesting. Taking Battle Caster and Practiced Spell Caster later on. [L1] Dodge, [L3] Practiced Spell Caster, [L6] Mobility, [L9] Battle Caster. If you make it a human you can get those feats set even earlier.

A problem with taking any other class that does not advance your caster levels such as Barbarian, Scout, or Paladin for your build means that by 20th (assuming you are worried about that) is that you will be losing 1 caster level per non caster advancing class you take as Practiced Spell Caster will compensate for the lost levels while taking Swift Blade - something to consider.