A 89 Beyond increasing your number of HD, and in 1st party 3.5 D&D, the most accessible (and generally, the only) way is the Primary Contact feat from Cityscape, giving you a single rank beyond your maximum.

Additionally, the Codex Anathema (LoM p 214) grants 5 ranks Knowledge (dungeoneering) and 2 ranks each of Knowledge (arcana) and (the planes). Yenejg Togan's Planar Syllabus (Dungeon 88 p 104) grants 6 ranks in Knowledge (the planes). The items don't say you can exceed your maximum, but don't say they cant, DM call.
Finally, the Illithid Savant PrC allows you to gain ranks beyond your maximum, but requires you to be an illithid.

In sanctioned 3rd party, there is at least Laborious Training from Ravenloft: Legacy of the Blood - Your maximum rank in any Intelligence-based skill equals 5 + your character level. Must have Int 13, Knowledge (any one) 5 ranks.