Christian wrote once into c.l.t.:

[BLT] can create (semi-transparent) bitmaps of text in arbitrary directions.

Try the following:
----
     package require BLT
     ::blt::bitmap compose myNewBitmap "this is a text" \
         -font "Arial 10 bold" \
         -rotate 90 \
         -justify left
     $myCanvas create bitmap 50 50 -bitmap myNewBitmap \
         -foreground blue \
         -anchor nw \
         ...
----

This works nicely.
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[RS]: Shouldn't the font rather be called Arial (or Helvetica, for even more platform-independence)?

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It's nice on the screen, but less nice on postscript output. 
Ability to rotate any standard canvas object would be a nice upgrade to Tk.
[IDG]

[RS]: see [photo image rotation] and [canvas rotation] (for lines and polygons)
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But blt-bitmaps cannot be destroyed, so the memory will be full of bitmaps when using this way too often.

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See [Rotated canvas text] for how some X servers can do this with pure Tk

[Category BLT]