While ToB prestige classes do advance both Swordsage and Warblade simultaneously, it's worth noting that Swordsage and Warblade levels only stack for the purposes of Initiator Level at a rate of 2 levels / IL (the same as any other multiclass IL progression). So Warblade 6 / Swordsage 8 has a Warblade IL of 6+(8/2) = 10 (max 5th level maneuvers) and a Swordsage IL of 8+(6/2) = 11 (max 6th level maneuvers). Since you need IL17 to get 9th level maneuvers for a given initiator class, you can only take 6 levels of any other class or prestige class (not counting ToB maneuver granting prestige classes). This means a maximum of Warblade 6 / Swordsage 6 / PrC 8.
I would be hesitant more than 4 in Swordsage (it's only a 3/4 BAB class, 5th gives you 1 maneuver known and +1 initiative but loses a BAB). Note that due to rounding, you should typically go for an even number of multiclass levels. That said, Swordsage 6 only gives you 1 (swordsage) maneuver known and +1 to all saves over Swordsage 5, so it may be that the benefit you'd get from a particular level of a PrC outweighs this. Warblade 5 offers a bonus feat (which can help with PrC Prereqs)
As for which PrCs are worth looking into, for a TWFer Bloodclaw Master is hard to overlook. You'll only want 2 or 3 levels, but BcM2 negates the penalty for TWFing, while 3 is the best cutoff in terms of maneuvers/stances known. Master of Nine gives an obscene amount of maneuvers known and readied, but it requires maneuvers from a wide range of schools (no problem) and has 5 feat prereqs. 2 of these are useful, one is situational, and 2 are feat taxes. Thankfully, one of them is on the Warblade bonus feat list.
One interesting option, if you have a wizard or sorcerer in the group, is to go with unarmed strikes. Superior Unarmed Strike gives you monk progression -4. Taking a 1 level dip in Fist of the Forest (Complete Champion) upgrades this to monk progression (except for level 20, where you're still 2d8). Get your wizard to cast Greater Mighty Wallop on you (1 hour/level, increases weapon size by 1 category/4 levels, giving you 8d8 damage at level 16). Greater Two weapon Fighting gives you 7 attacks, Raging Mongoose (Tiger Claw 8) increases this to 11, haste to 12, and Time Stands Still (Diamond Mind 9) doubles this to 24 attacks, each dealing 8d8 + whatever damage. Note that you have to spend a round not using any maneuvers between each use of this (although you can still full attack normally).
The build for this requires you to be human and take 2 flaws.
Swordsage 4-5 / Warblade 5 / Fist of the Forest 1 / Bloodclaw Master 4-5 / Master of Nine 5;Alternatively,
Swordsage 4 / Warblade 5 / Barbarian 1 / Fist of the Forest 1 / Bloodclaw Master 4 / Master of Nine 5 (gains pounce, but incurs Multiclass XP penalties).
Feats: Great Fortitude, Power Attack, Improved Unarmed Attack, Improved / Greater / TWF, Adaptive Style, Dodge, Blind-Fight, Improved Initiative, Superior Unarmed Strike.
I leave the exact ordering of the levels, maneuvers, and feats taken as an exercise for the reader. It can be done, I'm just not sure my approach is optimal.
This will get you level 9 maneuvers (using Warblade mechanics for maneuvers granted by PrCs), penalty free TWF with the ability to add 4 attacks to a full attack as a swift action, the to make two full attacks in a round, Wis and Con to AC, Int to Ref saves, and a few other things. That said, you're rather MAD, so those ability-to-defence features aren't as good as they sound. You'll need at least int 12 to make the skill prereqs, and you need at least 19 dex for GTWF. You'll want high Str/Dex/Con, mid Wis/Int, dump Cha. Also note that this build is EXTREMELY feat starved. You'll need a reasonably high point buy or stat roll just to make up for the loss of Weapon Finesse. Alternatively, you may need to consider giving up Greater TWF for Weapon Finesse...
Another interesting option is to go with a BardBlade Build. A basic rundown can be found
Here. Begin by taking the Bard Inspire Courage ability, buff it with items and the Dragonfire Inspiration line of feats (Dragon Magic) and Word of Creation (exalted; Book of Exalted Deeds), possibly also taking the feat Song of the White Raven to stack your Bard and Warblade levels for the purpose of IC (although this is not necessary, as I will soon show). You end up with +8-12d6 sonic damage per attack. Then add on the Warblade ability to put out a LOT of attacks per round. Add a one-level Barbarian dip for pounce (unless your DM is using the multiclass xp penalty rules) and blend everything in sight. This can also be combined with Sublime Chord and Jade Pheonix Mage to create a build with slightly lower inspire courage bonuses but with respectable spellcasting. IIRC you need to choose between 9th level spells or maneuvers; you can't get both pre-epic.