The Nintendo DSi uses the same title scheme and update servers as the Wii, but they introduced a new (currently unknown) common-key for the DSi title decryption.
The following titles have been seen:
00030004: Downloadable "DSiWare" titles
484e474a ('HNGJ'), 4b41414a ('KAAJ'), 4b41444a ('KADJ'), 4b414d4a ('KAMJ'),
4b44394a ('K9DJ'), 4b47554a ('KGUJ'), 4b4d394a ('KM9J'), 4b4d464a ('KMFJ'),
4b4d534a ('KMSJ'), 4b4e444a ('KNDJ'), 4b4e524a ('KNRJ'), 4b50364a ('KP6J'),
4b54504a ('KTPJ'), 4b55574a ('KUWJ')
00030005: 484e494a ('HNIJ')
0003000f: 484e4c4a ('HNLJ'), 484e4341 ('HNCA')
00030015: 484e464a ('HNFJ') -- apparently the "firmware"
00030017: 484e414a ('HNBJ')
As with on the Wii, the TMD for these titles may be fetched at e.g. http://nus.cdn.t.shop.nintendowifi.net/ccs/download/0003000f484e4c4a/tmd.
The official list is located here : http://www.nintendo.co.jp/ds/dsiware/titlelist.html
Each game specific url uses above 4 letter code.