Output a number in PrettyFont
k (118 117 72 71 69 66 chars)

I haven't made much of an effort to golf this yet but it achieves the desired horizontal output in not too many chars:

-1'" "/:'+(5 4#/:4 20#"# "@,/0b\:'0x066609ddd806db00e8e0)"I"$'0:0;


Takes input from stdin, prints output to stdout.

edit: By implementing a form of compression on the output "bitmap", I've reduced it to 72. The bitmap is now built by converting  64bit ints to binary and mapping the 0s and 1s to "#" or " ". I could do it from hex like a few of the other solutions but I think this would end up longer. Turns out hex is better.

Sample output for 012301:

####  ##  #### #### ####  ##
#  #   #  #  #    # #  #   #
#  #   #    #   ### #  #   #
#  #   #   #      # #  #   #
####  ### #### #### ####  ###


//edit: -6 char