Here is a brief list of php4 modules that come standard with our shared/sdx/reseller servers:

bcmath
calendar
ctype
curl
dom
domxml
exif
ftp
gd (with FreeType)
gettext
iconv
imap
mbstring
mbregex
mcrypt
mhash
mm
mysql
mysqli
openssl
overload
pcre
pdflib
pear
posix
pspell
sablot
session
sockets
standard
tokenizer
wddx
xml
xmlrpc
xslt
zip
zlib
Zend Optimizer

Note: ioncube can be installed by user within their account folders and usually comes with encoded applications.

If you need any other module that is officially supported by php, or one of the above module is missing from your server, please open a support ticket and we can evaluate if it is possible to install it.