Henk Wesseling (Divide and Rule: The Partition of Africa, 1880-1914, The European Colonial Empires 1815-1919) has written some of the better books on the Scramble era, although arguably Pakenham's The Scramble for Africa is more "pop-readable." If your interest is in depth, Wesseling's Divide and Rule would still be my one-volume recommendation. There are a few others (for example, Muriel Chamberlain's "Seminar Study" on the era) but those are the big ones on my bookshelf, and chapters from Wesseling are what I assign in courses.