I'd say most (if not all) of the Email, Email Date, Subscriber, and Sender personalization strings are included -- as are any attributes or data extension column names passed over in the send context. That is as long as you're using the CloudPageURL function to arrive at the page from an email.
+--------------------+
| Email Date Strings |
+--------------------+
| xtmonth |
| xtmonthnumeric |
| xtday |
| xtdayofweek |
| xtyear |
| xtshortdate |
| xtlongdate |
+--------------------+
+-----------------------+
| Email Data Strings |
+-----------------------+
| emailname_ |
| _emailid |
| _messagecontext |
| _replycontent |
| _IsTestSend |
| jobid |
| _JobSubscriberBatchID |
| _PreHeader |
| _DataSourceName |
| _listname |
+-----------------------+
+-------------------------+
| Subscriber Data Strings |
+-------------------------+
| emailaddr |
| firstname_ or firstname |
| lastname_ or lastname |
| subscriberid |
| _subscriberkey |
| listid |
| list_ |
| listsubid |
| _messagetypepreference |
+-------------------------+
+---------------------+
| Sender Data Strings |
+---------------------+
| replyname |
| replyemailaddress |
| memberid |
| member_busname |
| member_addr |
| member_city |
| member_state |
| member_postalcode |
| member_country |
+---------------------+