No one has mentioned the Med / Octamed family. The Amiga version just got a minor update.
Many versions of PShop would not load IFF files above 256 colors. Hope that's changed.
Some PC programs look for the .lbm extension instead of .iff.
Ulead's PhotoImpact handles 24bit IFF files very nicely. Several members of the Kansas City Users Group like P-I for its great power & low price. (under $100US, sometimes way under)