arena_warehouse_v2 http://forums.tf2maps.net/downloads.php?do=file&id=4980 -looks good, large open map great for pouncing!
arena_ruins_a3 http://forums.tf2maps.net/downloads.php?do=file&id=1223 -lots of dark areas with low-wide corridoors
arena_timberworks_b2a http://forums.tf2maps.net/downloads.php?do=file&id=2143 -interesting map, got a train, water and saws all sorts!
arena_dam-it_b1 http://forums.tf2maps.net/downloads.php?do=file&id=1847 -great map and concept, spawns are open which might be a problem if hidden can move before red team
arena_concord_b3 http://forums.tf2maps.net/downloads.php?do=file&id=2002 -very cool map, has a great death-pit area under the map where the health is
arena_cow2_a4 http://forums.tf2maps.net/downloads.php?do=file&id=4972 -moo, but seriously this would be fun :)
dropbox link: https://dl.dropbox.com/u/14737258/custom_arena_maps.zip