I keep a very detailed spreadsheet. Page one is wagers with a lot of the same data that InSpades describes. Date, league, wager details. I have a lot of little codes I've developed.
I also categorize bets into types (gambling-handicapping, gambling-mathematical, arbs, sides/middles, bonuses - I have single character codes for each). I also have fields for start time and rotation number (which is handy for ncaab and ncaaf) and also a column for who I'm cheering for. I don't know if that sounds funny but I place a lot of bets and can't always remember.
I have codes for all the many books I use. For my situation, it's important to follow-up that everything has been graded properly. There's too much going on to remember everything.
The next page is for banking. Deposits/withdrawals, monthly tracking of profits.
And I've got a number of pages for ongoing research and then some archives of bets and banking from past years. It is a big, extremely important file that I wouldn't want to lose and I e-mail copies every week to two different associates as disaster insurance.