import lxml.html
html = lxml.html.parse('http://materials.uzmarketing.com/postcards/')
sizes = tree.xpath('//*[@id="prductsize"]/div/div/ul/li')
print sizes

>>> import lxml.html
>>> 
>>> tree = lxml.html.parse('http://materials.uzmarketing.com/postcards/')
>>> sizes = tree.xpath('//*[@id="prductsize"]//option/text()')
>>> print sizes
['1.5" x 7"', '2" x 6"', '2" x 8"', '2.5" x 2.5"', '3" x 4"', '3" x 5"', '3.5" x 5"', '4" x 12"', '4" x 4"', '4" x 5"', '4" x 6" (Standard)', '4" x 9"', '4.25" x 11"', '4.25" x 2.75"', '4.25" x 3.66"', '4.25" x 5.5"', '4.25" x 6"', '4.25" x 9"', '4.5" x 12" (EDDM Eligible)', '4.75" x 4.75"', '5" x 7"', '5.5" x 2.125"', '6" x 11"', '6" x 9"', '6" x 12" (EDDM Eligible)', '6.25" x 11"', '6.25" x 9"', '6.5" x 9" (EDDM Eligible)', '6.5" x 12" (EDDM Eligible)', '8" x 5"', '8.5" x 2.75"', '8.5" x 3.5"', '8.5" x 3.667"', '8" x 6.5" (EDDM Eligible)', '8.5" x 4"', '8.5" x 5.5"', '8.5" x 6"', '8.5" x 7" (EDDM Eligible)', '8.5" x 7.5"', '9" x 11" (EDDM Eligible)', '9" x 12" (EDDM Eligible)', '8.5" x 11" (EDDM Eligible)']
>>>