I don't think I used nicknames prior to Gen IV.
In Diamond I used typical appearance/type-relevant names like "Flame", "Cloud", "Flora" and "Ocean". In Platinum I used Japanese and Korean singers (real, stage & nick) names like "Tomo", "Ryosuke", "Taeyang" and "Bom". In SoulSilver I'm being lazy and just using Diamond's technique again except with Japanese words instead of English. No doubt Black will be a mix of the last two.
So nothing unique, but it keeps me happy.