165 pointings of the Wide Field Camera on the INT in V and i yield 7 million stars with photometry that identifies RGB stars in M31 halo -- out to 80kpc (6 degrees). As for the MW, the M31 halo seems to have significant substructure. (INT news page: o-link).
The result of stacking (after first scaling by Rd) 1047 edge on spirals galaxies from the SDSS (Zibetti et al: o-link). The i-band contours in surface brightness are 29.5, 28.5, 27.5, 25.5, 23.5, 21.5 mag/ss. The excess light reveal a stellar halo. Data fro the other bands suggest it is quite red in color. These authors conclude that the data support the early formation of halos by the merger of dwarfs.