Round, square and rectangles, Nortek has got ya covered (well at least your posts that is)

Copper Piling cap cone shaped for decks & docks
$39.95 - $99.95
Denali Square & Rectangle Post Cap 1.5" drop
Sedona Round Natural Copper Post Cap with 1" drop
$10.25 - $92.65
New! -
Tiara Custom cap for irregular shaped posts
Tiara Round Natural Copper Post Cap with 2" drop
$26.20 - $136.45