Note that some of the species has a link where you can see a picture of one.
Sciurinae
Ammospermophilus A. harrisii - Harris Antelope Squirrel; southwest USA
A. insularis
A. interpres - Texas Antelope Squirrel; Texas
A. leucurus - White-tailed Antelope Squirrel; Southwest USA
A. nelsoni - Nelson's Antelope Squirrel (I think you need those 3D glasses to see this one); Southwest USA
Atlantoxerus A. getulus
Callosciurus C. adamsi
C. albescens
C. baluensis
C. caniceps
C. erythraeus - Golden-Backed Squirrel; Indochina, Taiwan, Japan
C. finlaysonii
C. inornatus
C. melanogaster
C. nigrovittatus
C. notatus
C. orestes
C. phayrei - Phayre's Squirrel; Indochina, Taiwan
C. prevostii - Prevost Squirrel; Indonesia, Malaysia
C. pygerythrus
C. quinquestriatus
Cynomys C. gunnisoni - Gunnison's Prairie Dog; New Mexico, Colorado, Arizona
C. leucurus
C. ludovicianus - Black-tailed Prairie Dog; Midwestern USA
C. mexicanus
C. parvidens
Dremomys D. everetti
D. lokriah
D. pernyi
D. pyrrhomerus
D. rufigenis
Epixerus E. ebii
E. wilsoni
Exilisciurus E. concinnus
E. exilis
E. whiteheadi
Funambulus F. layardi
F. palmarum
F. pennantii - Indian Palm Squirrel (India); Photo by Bert Wells.
F. sublineatus
F. tristriatus
Funisciurus F. anerythrus
F. bayonii
F. carruthersi
F. congicus
F. isabella
F. lemniscatus
F. leucogenys
F. pyrropus - Red-footed Tree Squirrel; Africa
F. substriatus
Glyphotes G. simus
Heliosciurus H. gambianus - Gambian Sun Squirrel; Africa
H. mutabilis
H. punctatus
H. rufobrachium
H. ruwenzorii
H. undulatus
Hyosciurus H. heinrichi
H. ileile
Lariscus L. hosei
L. insignis
L. niobe
L. obscurus
Marmota M. baibacina
M. bobak
M. broweri
M. caligata - Hoary Marmot; northwestern USA
M. camtschatica
M. caudata
M. flaviventris - Yellow-bellied Marmot; northwestern USA
M. himalayana
M. marmota - Alpine Marmot; Europe
M. menzbieri
M. monax - Woodchuck; eastern USA
M. olympus - Olympic Marmot; northwest Washington state
M. sibirica
M. vancouverensis - Vancouver Island Marmot; Vancouver is. (western Canada)
Menetes M. berdmorei
Microsciurus M. alfari
M. flaviventer
M. mimulus
M. santanderensis
Myosciurus M. pumilio
Nannosciurus N. melanotis
Paraxerus P. alexandri
P. boehmi
P. cepapi - Smith's Bush Squirrel; Africa
P. cooperi
P. flavovittis
P. lucifer
P. ochraceus
P. palliatus
P. poensis
P. vexillarius
P. vincenti
Prosciurillus P. abstrusus
P. leucomus
P. murinus
P. weberi
Protoxerus P. aubinnii
P. stangeri
Ratufa R. affinis
R. bicolor - Black Giant Squirrel; southeast Asia
R. indica
R. macroura
Rheithrosciurus R. macrotis
Rhinosciurus R. laticaudatus
Rubrisciurus R. rubriventer
Sciurillus S. pusillus
Sciurotamias S. davidianus
S. forresti
Sciurus - Largest Genus of Tree Squirrels (also includes pictures)
S. aberti
S. aestuans
S. alleni
S. anomalus
S. arizonensis
S. aureogaster
S. carolinensis
S. colliaei
S. deppei
S. flammifer
S. gilvigularis
S. granatensis
S. griseus
S. ignitus
S. igniventris
S. lis
S. nayaritensis
S. niger
S. oculatus
S. pucheranii
S. pyrrhinus
S. richmondi
S. sanborni
S. spadiceus - South Amazon Red Squirrel (I think); Bolivia, Brazil
S. stramineus
S. variegatoides
S. vulgaris
S. yucatanensis
Spermophilopsis S. leptodactylus
Spermophilus S. adocetus
S. alashanicus
S. annulatus
S. armatus - Uinta Ground Squirrel; Utah
S. atricapillus
S. beecheyi - California Ground Squirrel; far western USA
S. beldingi - Belding's Ground Squirrel; California, Nevada
S. brunneus
S. canus
S. citellus
S. columbianus - Columbian Ground Squirrel; British Columbia
S. dauricus
S. elegans - Wyoming Ground Squirrel; Wyoming, Idaho, Montana
S. erythrogenys
S. franklinii
S. fulvus
S. lateralis - Golden Mantled Ground Squirrel; western USA
S. madrensis - Sierra Madre Mantled Ground Squirrel; southwestern USA
S. major
S. mexicanus - Mexican Ground Squirrel; Texas, Mexico
S. mohavensis - Mojave Ground Squirrel; Western USA, Mexico
S. mollis
S. musicus
S. parryii - Arctic Ground Squirrel; Alaska, Siberia, Canada
S. perotensis
S. pygmaeus
S. relictus
S. richardsonii - Richardson's Ground Squirrel; Alberta, Montana, Dakotas
S. saturatus - Cascade Mantled Ground Squirrel; northern Rockies
S. spilosoma - Spotted Ground Squirrel; western USA and plains states, Mexico
S. suslicus - European Souslik; eastern Europe
S. tereticaudus
S. townsendii - Townsend's Ground Squirrel; western USA
S. tridecemlineatus - Thirteen lined Ground Squirrel; midwestern USA
S. undulatus
S. variegatus - Rock Squirrel; Arizona, New Mexico, Colorado
S. washingtoni
S. xanthoprymnus
Sundasciurus S. brookei
S. davensis
S. fraterculus
S. hippurus
S. hoogstraali
S. jentinki
S. juvencus
S. lowii
S. mindanensis
S. moellendorffi
S. philippinensis
S. rabori
S. samarensis
S. steerii
S. tenuis
Syntheosciurus S. brochus
Tamias T. alpinus
T. amoenus --Yellow pine chipmunk; northwest USA, southwest Canada
T. bulleri
T. canipes
T. cinereicollis
T. dorsalis
T. durangae
T. merriami - Merriam's Chipmunk
T. minimus - Least Chipmunk; southern Canada, northwestern USA
T. obscurus
T. ochrogenys
T. palmeri
T. panamintinus - Panamint Chipmunk
T. quadrimaculatus
T. quadrivittatus - Colorado Chipmunk; Colorado, New Mexico, Utah
T. ruficaudus
T. rufus
T. senex
T. sibiricus - Siberian Chipmunk; Russia, Korea, China, Japan
T. siskiyou
T. sonomae
T. speciosus - Lodgepole Chipmunk
T. striatus - Eastern Chipmunk; Eastern USA
T. townsendii - Townsend's Chipmunk; Oregon and Washington
T. umbrinus - Uinta Chipmunk; Utah
Tamiasciurus T. douglasii - Douglas Squirrel; British Columbia, Washington, Oregon, California
T. hudsonicus - American Red Squirrel; Canada, northern and western USA
T. mearnsi
Tamiops T. macclellandi - Himalayan Striped Squirrel
T. maritimus
T. rodolphei
T. swinhoei
Xerus X. erythropus - Cape Ground Squirrel; South Africa
X. inauris - Unstriped Ground Squirrel; Africa
X. princeps
X. rutilus
Petauristinae
Aeretes A. melanopterus
Aeromys A. tephromelas
A. thomasi
Belomys B. pearsonii
Biswamoyopterus B. biswasi
Eupetaurus E. cinereus - Wooly Flying Squirrel; India
Glaucomys G. sabrinus - Northern Flying Squirrel; Canada, northern and western USA
G. volans - Southern Flying Squirrel; Eastern USA, Mexico
Hylopetes H. alboniger
H. baberi
H. bartelsi
H. fimbriatus
H. lepidus
H. nigripes
H. phayrei
H. sipora
H. spadiceus
H. winstoni
Iomys I. horsfieldi
I. sipora
Petaurillus P. emiliae
P. hosei
P. kinlochii
Petaurista P. alborufus
P. elegans
P. leucogenys - Japanese Giant Flying Squirrel; Japan
P. magnificus
P. nobilis
P. petaurista - Red Giant Flying Squirrel; southeast Asia
P. philippensis
P. xanthotis
Petinomys P. crinitus
P. fuscocapillus
P. genibarbis
P. hageni
P. lugens
P. sagitta
P. setosus
P. vordermanni
Pteromys P. momonga - Japanese Pygmy Flying Squirrel (Awww! Cuuute!); Japan
P. volans - Siberian Flying Squirrel; Finland to Japan
Pteromyscus P. pulverulentus
Trogopterus T. xanthipes
Special Note: Please be aware that not all of these pictures are mine. I borrowed them from other websites and I downloaded them to my homepager.