I use an Excel spreadsheet and maintain the following fields: type, year, brand/description, card#, team pictured, a "HOF" flag, a "notes" field, Beckett BV and the date I looked up the BV. For football and basketball, I also have a college field.
The "type" field includes... base, RC, SP, parallel, insert, refractor, serial-numbered, jersey, auto, multi-GU, jersey-auto, patch, QUAD, oddball, etc.
In the "note" field I make comments like "heavy crease", "mis-cut" or info about the card like the subset "team leaders" or the serial number.
I don't add every "base" card (that would be insane) but have some in my database, mostly vintage of higher value. My base singles are kept in numerical order by year, set. I store all my non-base cards by year in set/card number order. This all makes if fairly easy and fast to find items.
Then, using filters on every column, I can quickly list, "game used, autographs, Jets, Rutgers, and HOFers only".
I've got separate tabs in one Excel sheet for each sport. I suppose you could make it one database by adding "sport" as another column. I don't because I have over 30K cards in my database total and that would slow down the filtering some.
I've thought about adding a "serial #" field alone so I could also quickly filter serial #d GU from non ser #d.
The toughest part is keeping it current. You have to have discipline with each trade. Before I package cards for shipment, I delete the record from the database. I do a pretty good job but occasionally make an error... it's usually that 2:30 a.m. trade when my mind isn't sharp!
I usually do a complete inventory about twice a year to fix the mistakes... literally going through the 30K cards, one-by-one. It sounds brutal but isn't bad while watching a baseball game particularly if there aren't a lot of errors!
I generally don't make trade pages (websites), because for some reason that has been harder for me to keep them current. You also lose flexibility with searches plus webspace is an issue with the size of lists I'd have. The other reason, and some of you may not like this, is that I don't care for cherry pickers!
If anyone is interested in this Excel spreadsheet, I'd be happy to make an empty one and send it to you. PM me your e-mail.