The Field Guide to the Birds of East Africa by Stevenson and Fanshawe is extremely useful for this part of Africa and covers Kenya, Tanzania, Uganda, Rwanda and Burundi. The first edition was published in 2002 and a second edition is due later in 2012.
In addition, the Zimmerman et al is very good but only covers Kenya and those additional species which are also found in northern Tanzania. However, make sure to choose carefully between the hardback and more portable (and revised) paperback version. The hardback version is not one to carry in the field but the softcover does lack some detail!
Birds of Africa south of the Sahara also covers all the species found in the East Africa region.
Helm Field Guide covering Kenya, Tanzania, Uganda, Rwanda and Burundi. The first complete guide to this region. 3400 images of 1388 species illustrated on 287 superb new colour plates by Brian Small, John Gale and Norman Arlott. The text plus distribution map and the illustrations for each species are on facing pages. 632 pages.
Designed specifically for use in the field, this is a portable version of the highly-acclaimed Birds of Kenya and Northern Tanzania. This updated edition covers 6 additional species.
"Birders visiting Kenya have been waiting a long time for a really good identification guide to the rich avifauna of this incomparable country. They need wait no longer. This magnificent book is everything one could wish for." - British Birds.
Second edition, including 500 new images and 400 updated distribution maps. Unrivalled coverage of African birds in a single volume. 2129+ species covered with an additional 101 vagrants briefly described. Revised to reflect the latest changes in taxonomy. Species descriptions give precise identification features highlighting differences between similar species as well as briefly reporting habitat, status and call. Annotated illustrations portray distinctive plumages as well as diagnostic flight patterns and major geographic variants where applicable.
Field identification guide, with the text highlighting the diagnostic features for each species. For those species that are sexually dimorphic, have both breeding and non-breeding plumages, or in which the juvenile plumage differs markedly from that of the adult, more than one photograph has been included. A thumbnail silhouette and a distribution map are given for each species. 144 pages.
80 sites detailed with maps and many line drawings. Essential information for locating Tanzania's special birds. 303 pages.
Vocalisations of 99 common species, each indexed but not announced.