With the advancement of Internet Technology, increasing number of electronic marketplaces and online auction houses provides real-time transaction services for buyers and sellers regardless of their geographical locations. Easy access to these services has also fueled the need for automating the overall negotiation and decision making process. The annual Trading Agent Competition (TAC) is an international forum designed to provide a competitive benchmark for the trading agents developers around the world. The first TAC was held in July, 2000. In the TAC-Classic category, travel agents compete against each other to assemble travel packages on behalf of several clients. The objective of the travel agent is to maximize the total satisfaction of its clients. During the competition, travel agents may perform three crucial tasks: allocation of resources according to the clients' preferences, prediction of air ticket and hotel prices, and bidding in respective auctions for the required goods. In this paper, we review the algorithms, techniques and heuristics used by the agents which have the highest scores in the last six years of tournaments.