I don't know of any bus lists, so I made one. If anyone wants a list of another fansite, just post below. :)
Remember that you can use Ctrl+F to search for keywords within the list. ;)
Also, Simtropolis had a lot, so I sub-divided them geographically or by type. :P
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SimCity Central
SCC Bus (http://www.simcitycentral.net/forums/showthread.php?tid=101)
Canadian Edmonton GMC Bus (http://www.simcitycentral.net/forums/showthread.php?tid=157)
Canadian Toronto Bus (http://www.simcitycentral.net/forums/showthread.php?tid=160)
Dutch Connexxion Bus (http://www.simcitycentral.net/forums/showthread.php?tid=88)
Dutch Streek Bus (http://www.simcitycentral.net/forums/showthread.php?tid=159)
Australian ACTION Bus (http://www.simcitycentral.net/forums/showthread.php?tid=87)
American New Jersey Transit Bus (http://www.simcitycentral.net/forums/showthread.php?tid=158)
Canada Mississauga Bus (http://www.simcitycentral.net/forums/showthread.php?tid=156)
Swedish Bus (http://www.simcitycentral.net/forums/showthread.php?tid=105)
Modern Double Decker Bus (http://www.simcitycentral.net/forums/showthread.php?tid=100)
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Tout Sim Cities
Perpignan Bus (http://www.toutsimcities.com/downloads.php?view=1043)
Paris Agora S Bus Irisbus (http://www.toutsimcities.com/downloads.php?view=1103)
Orange Bus (http://www.toutsimcities.com/downloads.php?view=1788)
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Simtropolis
NYC MTA Buses
NYBT NYC MTA bus - MCI D4500 (http://www.simtropolis.com/forum/files/file/23074-nybt-nyc-mta-bus-mci-d4500/)
NYBT NYC MTA bus - New Flyer C40LF (http://www.simtropolis.com/forum/files/file/22717-nybt-nyc-mta-bus-new-flyer-c40lf/)
NYC MTA bus - Orion V (http://www.simtropolis.com/forum/files/file/22084-nyc-mta-bus-orion-v/)
NYC MTA bus - Orion VII (http://www.simtropolis.com/forum/files/file/22161-nyc-mta-bus-orion-vii/)
Other American
MBTA Transit Pack (http://www.simtropolis.com/forum/files/file/13560-mbta-transportation-set/)
GMC RTS 1990 New York and New Jersey (http://www.simtropolis.com/forum/files/file/22154-gmc-rts-1990-new-york-and-new-jersey/)
SEPTA Bus Pack N-40 (http://www.simtropolis.com/forum/files/file/24024-septa-bus-pack-nf40/)
BART Bus (http://www.simtropolis.com/forum/files/file/11783-bart-bus/)
Toronto (TTC) Buses
TTC City Flyer Bus V2 (http://www.simtropolis.com/forum/files/file/14688-ttc-city-bus-flyerversion-2-update/)
Toronto TTC Bus Pack (http://www.simtropolis.com/forum/files/file/22183-toronto-ttc-bus-pack/)
Other Canadian Buses
Ottawa Bus (http://www.simtropolis.com/forum/files/file/21182-ottawa-busses/)
Montreal Bus 3 (http://www.simtropolis.com/forum/files/file/21174-montreal-bus-3/)
Sydney, Australia Buses
Sydney Transit Bus (http://www.simtropolis.com/forum/files/file/21021-sydneytransitbus/)
Sydney Transit Bus V2 (http://www.simtropolis.com/forum/files/file/23104-sydney-transit-bus-2/)
Dutch Buses
Dutch BBA Bus (http://www.simtropolis.com/forum/files/file/23187-dutch-bba-bus/)
Dutch City Bus Rotterdam RET Citaro (http://www.simtropolis.com/forum/files/file/21125-dutch-city-bus-rotterdam-ret-citaro/)
Sao Paulo/Brazil Buses
Sao Paulo Buses Articulated (http://www.simtropolis.com/forum/files/file/23042-sao-paulo-busses-v5-articulated/)
Sao Paulo Buses V4 (The Last 5) (http://www.simtropolis.com/forum/files/file/22431-sao-paulo-busses-v4-the-last-5/)
Sao Paulo Intermunicipal Buses (http://www.simtropolis.com/forum/files/file/21740-sao-paulo-intermunicipal-busses/)
Sao Paulo Buses (http://www.simtropolis.com/forum/files/file/21730-sao-paulo-busses/)
Intercity bus Belo Horizonte Brazil (http://www.simtropolis.com/forum/files/file/25267-intercity-bus-belo-horizonte-brazil/)
Beijing Buses
Beijing Jinghua Turquoise bus 1HD512 (http://www.simtropolis.com/forum/files/file/25525-beijing-jinghua-turquoise-bus-1hd512/)
Beijing BRT 1HD512 (http://www.simtropolis.com/forum/files/file/25520-beijing-brt-1hd512/)
Asian Buses
TransJakarta Busway (http://www.simtropolis.com/forum/files/file/24213-transjakarta-busway/)
HK mini buses red (http://www.simtropolis.com/forum/files/file/23481-hk-mini-buses-red/)
HK New World First Bus (http://www.simtropolis.com/forum/files/file/21839-hk-new-world-first-bus/)
HK Kowloon Bus Number 41A (http://www.simtropolis.com/forum/files/file/21838-hk-kowloon-bus-no-41a/)
HK City Bus (http://www.simtropolis.com/forum/files/file/21835-hk-city-bus/)
Korean Style Low-Floor Bus (http://www.simtropolis.com/forum/files/file/23129-korean-style-low-floor-bus/)
School Buses
Replacement School Bus (http://www.simtropolis.com/forum/files/file/25717-replacement-school-bus/)
UDI School Bus (http://www.simtropolis.com/forum/files/file/25657-udi-school-bus/)
School Bus 1997 AmTran (http://www.simtropolis.com/forum/files/file/22008-school-bus-1997-amtran/)
Euro School Bus (http://www.simtropolis.com/forum/files/file/17353-euro-school-bus/)
Greyhound Buses
Greyhound Bus Skins (http://www.simtropolis.com/forum/files/file/13626-greyhound-bus-skins/)
MCI E4500 Greyhound Bus Lines (http://www.simtropolis.com/forum/files/file/22177-mci-e4500-greyhound-bus-lines/)
Volvo Buses
Volvo 9700 Shorter Version (Additional) (http://www.simtropolis.com/forum/files/file/23394-volvo-9700-shorter-version-additional/)
Volvo 9700 twin axle long bus (http://www.simtropolis.com/forum/files/file/22338-volvo-9700-twin-axle-long-bus-automata/)
Double Decker Buses
Sightseeing Bus Automata +Lots (http://www.simtropolis.com/forum/files/file/23253-sightseeing-buses-automata-lots/)
London Modern Double Decker Bus (http://www.simtropolis.com/forum/files/file/10921-london-modern-double-decker-bus/)
London Routermaster Bus (http://www.simtropolis.com/forum/files/file/4548-london-routemaster-bus/)
Miscellaneous
Scania K114 Irizar (http://www.simtropolis.com/forum/files/file/22409-scania-k114-irizar/)
Mega Bus 2 (http://www.simtropolis.com/forum/files/file/22184-mega-bus-2/)
Mega Bus (http://www.simtropolis.com/forum/files/file/22179-mega-bus/)
NTA Modern Bus (http://www.simtropolis.com/forum/files/file/19248-nta-modern-bus/)
Star Motors Old Bus (http://www.simtropolis.com/forum/files/file/18450-star-motors-old-bus/)
SMP UK First Bus Mod (http://www.simtropolis.com/forum/files/file/17715-smp-uk-first-bus-mod/)
MAN NL 223 (http://www.simtropolis.com/forum/files/file/16245-man-nl-223/)
Brilliant! &apls
What a great surprise... :D