Delegates are expected to make their own arrangements for accommodation. A large number of hotels are available in Addis Ababa. While the organizers do not recommend any hotel in particular, the following options are available.
View list of hotels
Download AGIS ’11 Information for Participants (PDF), and see section “Hotel Accommodation” for recommended hotels. It is a matter or urgency for you to arrange your visa (if travelling from abroad) and your hotel accommodation in advance of travelling.
You can find more hotel options on Wikitravel.