Is there currently a way to slide a texture around a 3d object for better alignment?
(if not, I will save it for the next wish list)
Ken Brilliant’s UV Mapping tutorial should give you some ideas for how this can be accomplished with Planar, Cylindrical or Spherical maps.
If your model has been mapped using a different method (such as in UVMapper or another application), then you can still adjust your texture position. Tool>Modifiers>Texture>AdjU and AdjV will move the texture incrementally horizontally or vertically. Simply set a value (range -10 to 10) and then press the Apply Adj button to tweak the coordinates. You may have to do this quite a few times if the texture needs to be moved dramatically. But it can be done. 
thanks, Aurick