1. He redrew the congressional district lines in Texas to possibly gain six more seats for the Republican majority when the lines weren't due to be redrawn for another eight years.
This speaks for itself. At first glance almost anyone who reads what he did would say it is unethical to change the boundries in order to win. Of course I don't know the reasons for why he changed those boundries, probably he would claim that the new districts better represented the voting pools. My guess is that he changed them solely to gain more republican seats in the House, but it is just that: a guess. However, it has been in the news a lot lately and most likely there is a legitimate reason to think what he did was unethical.
2. DeLay used lobbyist's and business' campaign and fund rasing money to cover his travel expenses to several places for non-congress related work, or as the media likes to say: junkets. As well as giving about $500,000 to his family for their help in the campaign with no documentation of what the rest of the family did to deserve that much money.
His daughter and wife were registered as empolyees for the campaign but the amount of money they earned was way more than necessary. This, of all the things he has done, I think, requires the ethics committee review. That is enough on this though.
3. Durring the Terri Schiavo media fiasco Tom DeLay was quoted as having said, "The time will come for the men responsible for this to answer for their behavior." This was said because federal judges refused to review the Schiavo case again even after a bill was passed by congress and signed by the President to reopen the case.
This situation is not quite as obvious as to why it is an ethical problem than the preceding two. The reason I think of this as a problem is because it shows how Tom DeLay and the republican majority are trying to abuse their powers and affect the Judicial branch of the government. It is not part of his duties as a legislator to try and force the judges to make legal decisions that have already been decided upon again, let alone threaten them when they do not take part in Schriavo case.