Splitting raster into smaller chunks using GDAL?

gdal_translate will work using the -srcwin or -projwin options.

-srcwin xoff yoff xsize ysize: Selects a subwindow from the source image for copying based on pixel/line location.

-projwin ulx uly lrx lry: Selects a subwindow from the source image for copying (like -srcwin) but with the corners given in georeferenced coordinates.

You would need to come up with the pixel/line locations or corner coordinates and then loop over the values with gdal_translate. Something like the quick and dirty python below will work if using pixel values and -srcwin is suitable for you, will be a bit more work to sort out with coordinates.

import os, gdal
from gdalconst import *

width = 512
height = 512
tilesize = 64

for i in range(0, width, tilesize):
    for j in range(0, height, tilesize):
        gdaltranString = "gdal_translate -of GTIFF -srcwin "+str(i)+", "+str(j)+", "+str(tilesize)+", " \
            +str(tilesize)+" utm.tif utm_"+str(i)+"_"+str(j)+".tif"
        os.system(gdaltranString)

My solution, based on the one from @wwnick reads the raster dimensions from the file itself, and covers the whole image by making the edge tiles smaller if needed:

import os, sys
from osgeo import gdal

dset = gdal.Open(sys.argv[1])

width = dset.RasterXSize
height = dset.RasterYSize

print width, 'x', height

tilesize = 5000

for i in range(0, width, tilesize):
    for j in range(0, height, tilesize):
        w = min(i+tilesize, width) - i
        h = min(j+tilesize, height) - j
        gdaltranString = "gdal_translate -of GTIFF -srcwin "+str(i)+", "+str(j)+", "+str(w)+", " \
            +str(h)+" " + sys.argv[1] + " " + sys.argv[2] + "_"+str(i)+"_"+str(j)+".tif"
        os.system(gdaltranString)

There's a bundled python script specifically for retiling rasters, gdal_retile:

gdal_retile.py [-v] [-co NAME=VALUE]* [-of out_format] [-ps pixelWidth pixelHeight]
               [-overlap val_in_pixel]
               [-ot  {Byte/Int16/UInt16/UInt32/Int32/Float32/Float64/
                      CInt16/CInt32/CFloat32/CFloat64}]'
               [ -tileIndex tileIndexName [-tileIndexField tileIndexFieldName]]
               [ -csv fileName [-csvDelim delimiter]]
               [-s_srs srs_def]  [-pyramidOnly]
               [-r {near/bilinear/cubic/cubicspline/lanczos}]
               -levels numberoflevels
               [-useDirForEachRow]
               -targetDir TileDirectory input_files

e.g:

gdal_retile.py -ps 512 512 -targetDir C:\example\dir some_dem.tif