Figured it out on my own. Posting it here for the benefit of others, it would be great if it was added to the integration help page:
[residence_country] =>
[payer_business_name] =>
[first_name] =>
[last_name] =>
[payer_email] =>
[payer_phone] =>
[payer_street] =>
[payer_city] =>
[payer_state] =>
[payer_zip] =>
[payer_country_code] =>
[address_name] =>
[address_business_name] =>
[address_phone] =>
[address_street] =>
[address_city] =>
[address_state] =>
[address_zip] =>
[address_country_code] =>
[address_country] =>
[payment_date] => 14:59:32 Aug 23, 2009 MST
[custom] =>
[mc_currency] => USD
[business] =>
[mc_gross] =>
[mc_shipping] =>
[tax] => 0
[txn_type] =>
[payment_type] =>
[invoice] =>
[buyer_ip] =>
[card_last_four] =>
[card_type] =>
[mailing_list_status] =>
[item_name1] =>
[item_number1] =>
[mc_gross_1] =>
[quantity1] =>
[num_cart_items] => 1
[txn_id] =>
[payment_status] => Completed
[pending_reason] =>
[item_name] =>
[item_number] =>
[quantity] => 1
[option_name1] =>
[option_selection1] =>
[option_name2] =>
[option_selection2] =>
[option_name3] =>
[option_selection3] =>
[mc_handling] => 0
[handshake] =>
[discount_codes] =>
[from_name] =>
[from_email] =>