List of shared (non-stacking) debuffs
Attack speed lowering (melee)
Deathknight [Frost Fever]: Caused by [Icy Touch], [Hungering Cold], glyphed [Howling Blast] and glyphed [Scourge Strike]. Can also be caused by using [Pestilence] on a nearby creature that already has Frost Fever. Increases casting time and melee and ranged attack intervals by 14% (20% fully talented with [Improved Icy Touch], a tier 1 Frost talent with 3 ranks).
Druid [Infected Wounds]: Tier 8 Feral Combat talent, 3 ranks, causes [Mangle], [Maul] and [Shred] to apply the Infected Wound debuff, which increases melee attack interval by 20% @ max rank, also reduces movement speed.
Paladin [Judgements of the Just]: Tier 9 Protection talent, 2 ranks, causes Judgements to increase melee attack intervals 20% @ max rank.
Warrior [Thunder Clap]: Reduces melee and ranged attack intervals by 10%, 20% when talented.
Shaman [Earth Shock]: Reduces melee and ranged attack intervals by 10%, 20% when talented.