Apart from AVOIDING stalemate, there is a second possible reason for
underpromotion to rook or bishop, as I learned from a recent article by Jan
Timman in New in Chess Magazine. He gives several studies in which
underpromotion on the contrary serves to BRING ABOUT a stalemate.

Here's a simple example, a study by Archakov and Zinar from 1985:
8/1p4P1/1P6/KP2p3/1Pkppp2/5ppp/1P6/8 w - - 0 0
White to play and draw.

1.g8B+!
After 1.g8Q+? Black's pawns (he still has all 8 of them!) would prevail.
1...Kd3 2.Bb3
and Black cannot prevent White from stalemating himself with 3.Ba4 and 4.b3.

For more examples see Timman's article in New in Chess 2003/5, page 93.

Tobi