contents of file1:

ETIAM......
SED........
MAECENAS...
DONEC......
SUSPENDISSE

contents of file2

Lorem....
Proin....
Nunc.....
Quisque..
Aenean...
Nam......
Vivamus..
Curabitur
Nullam...

paste file1 file2

ETIAM...... Lorem....
SED........ Proin....
MAECENAS... Nunc.....
DONEC...... Quisque..
SUSPENDISSE Aenean...
    Nam......
    Vivamus..
    Curabitur
    Nullam...

ETIAM...... Lorem....
SED........ Proin....
MAECENAS... Nunc.....
DONEC...... Quisque..
SUSPENDISSE Aenean...
            Nam......
            Vivamus..
            Curabitur
            Nullam...

paste file1 file2 | column -t

ETIAM......  Lorem....
SED........  Proin....
MAECENAS...  Nunc.....
DONEC......  Quisque..
SUSPENDISSE  Aenean...
Nam......
Vivamus..
Curabitur
Nullam...

paste file1 file2 | expand -t 13

paste file1 file2 | expand -t $((`wc -L file1|awk '{print $1}'` + 2))

awk '{if(length($0)>max)max=length($0)}
FNR==NR{s1[FNR]=$0;next}{s2[FNR]=$0}
END { format = "%-" max "st%-" max "sn";
  numlines=(NR-FNR)>FNR?NR-FNR:FNR;
  for (i=1; i<=numlines; i++) { printf format, s1[i]?s1[i]:"", s2[i]?s2[i]:"" }
}' file1 file2

# 2013-11-05 mike@diehn.net
# Invoke thus:
#   awk -f this_file file1 file2
# The result is what you asked for and the columns will be
# determined by input file order.
#----------------------------------------------------------
# No matter which file we're reading,
# keep track of max line length for use
# in the printf format.
#
{ if ( length($0) > max ) max=length($0) }

# FNR is record number in current file
# NR is record number over all
# while they are equal, we're reading the first file
#   and we load the strings into array "s1"
#   and then go to the "next" line in the file we're reading.
FNR==NR { s1[FNR]=$0; next }

# and when they aren't, we're reading the
#   second file and we put the strings into
#   array s2
{s2[FNR]=$0}

# At the end, after all lines from both files have
# been read,
END {
  # use the max line length to create a printf format
  # the right widths
  format = "%-" max "st%-" max "sn"
  # and figure the number of array elements we need
  # to cycle through in a for loop.
  numlines=(NR-FNR)>FNR?NR-FNR:FNR;
  for (i=1; i<=numlines; i++) {
     printf format, s1[i]?s1[i]:"", s2[i]?s2[i]:""
  }
}

paste file1 file2 | sed 's/^TAB/&&/'

# Invoke thus:
#   awk -F\t -f this_file file1 file2

# every time we read a new file, FNR goes to 1

FNR==1 {
    curfile++                       # current file
}

# read all files and save all the info we'll need
{
    column[curfile,FNR]=$0          # save current line
    nlines[curfile]++               # number of lines in current file
    if (length > len[curfile])
            len[curfile] = length   # max line length in current file
}

# finally, show the lines from all files side by side, as a table
END {
    # iterate through lines until there are no more lines in any file
    for (line = 1; !end; line++) {
            $0 = _
            end = 1

            # iterate through all files, we cannot use
            #   for (file in nlines) because arrays are unordered
            for (file=1; file <= curfile; file++) {
                    # columnate corresponding line from each file
                    $0 = $0 sprintf("%*s" FS, len[file], column[file,line])
                    # at least some file had a corresponding line
                    if (nlines[file] >= line)
                            end = 0
            }

            # don't print a trailing empty line
            if (!end)
                    print
    }
}