for the sake of info from the SRD:
Spider Swarm CR1
Bat Swarm CR2
Rat swarm CR2
Locust swarm CR3
Centipede swarm CR4
Hellwasp swarm CR8, DR 10/ Magic, Fire Resistance 10
or someone could finish this list from here:
http://realmshelps.dandello.net/cgi-bin/mainlist.plSwarm, Abyssal Ant Aberration Fiend Folio
Swarm, Bat Animal Monster Manual v.3.5
Swarm, Bonespider Outsider Dungeon #119
Swarm, Brood Keeper Larva Magical Beast Monster Manual III
Swarm, Centipede Vermin Monster Manual v.3.5
Swarm, Cinder Elemental Monster Manual III
Swarm, Cranium Rat Average Pack Magical Beast Fiend Folio
Swarm, Cranium Rat Greater Pack Magical Beast Fiend Folio
Swarm, Cranium Rat Lesser Pack Magical Beast Fiend Folio
Swarm, Death Scarab Undead Sandstorm
Swarm, Dread Blossom Plant Monster Manual III
Swarm, Ephemeral Undead Monster Manual III
Swarm, Ettercap Brood Aberration Dragon #343
Swarm, Hellwasp Magical Beast Monster Manual v.3.5
Swarm, Locust Vermin Monster Manual v.3.5
Swarm, Murder of Crows Animal Tome of Magic
Swarm, Needletooth Animal Monster Manual III
Swarm, Plague Ant Vermin Fiend Folio
Swarm, Rat Animal Monster Manual v.3.5
Swarm, Scarab Beetle Vermin Fiend Folio
Swarm, Scorpion Vermin Sandstorm
Swarm, Sheengrass Plant Web
Swarm, Shimmerling Fey Monster Manual III
Swarm, Spider Vermin Monster Manual v.3.5
Swarm, Sun Fly Outsider Book of Exalted Deeds
Swarm, Swamp Strider Vermin Monster Manual III
Swarm, Verx Aberration Dragon #281
Swarm, Viper Animal Fiend Folio
Swarm, Wasp Vermin Fiend Folio