So, you're a Rog3 so far.
Which would you rather concentrate on, sticking holes in people or being Mad Skillz Guy?
If you're going to Stick Holes in People, you could take Swa3 (for the free Weapon Finesse* and Int bonus to damage), Ftr 2 (two bonus feats), and Clr 2.  Why two levels of cleric?  Grave Strike, from Complete Adventurer, lets you sneak attack undead for one round.  Also, two levels of cleric rids you of massive multiclassing penalties.
Of course, going this route, you still won't have more than +2d6 in sneak attack damage, and your roguely skills are shot all to heck, but it'll give you the feats you need to enter Tempest and Invisible Blade.  Just not right away.
Let's see...you have TWF and Weapon Finesse now.  To enter Invisible Blade, you need WF: Dagger.  To enter Tempest**, you need Imp. Two-Weapon Fighting, Dodge, Mobility, and Spring Attack.  That's another six feats.  You can enter Invisible Blade starting at 7th level if you just keep taking Rogue.  Without using flaws to generate additional feats, though, you couldn't hit Tempest until Epic levels (or using your Rogue special abilities for feats, which is usually contraindicated).  Even with the above class build, the two bonus feats mean that you can't hit Tempest until 16th level at least.
I'd suggest just sticking with Rogue for now and taking WF: Dagger and going up the TWF tree.  When you feel like it, you can take Invisible Blade and get more fun sneak attack and bluffing bonuses.
Brad
* - Were you to go this way, beg the DM to let you un-take 3rd level and put Swa1 there, since that gives you Weapon Finesse for free.  That frees up a feat for WF: Dagger.
** - By all that is holy, this is a beautiful PrC.  Everyone who ever wanted to use two weapons at once should run out right now and pick up Complete Adventurer.