I am not a huge fan of most aikido books. Half of them are about putting the founder on a pedestal and proclaiming him to a an enlightened being. Good for him! Doesn't help me much though.
Another huge chunk is very dry technical logs, that I humbly suggest since the creation of you tube have become obsolete.
Now my favorite book about aikido is the Tai Chi Classics.
Tai Chi Classics
Now how can a tai chi book be an aikido book? Well I humbly suggest everyone get past the silly name game thing we play and realize what we are all shooting for, maximum efficiency with minimum effort. Get information where ever you can.