If you know how to work in MS Access and are able to make a nice interface that's the best option. I started using Access myself, but now I'm using MS Excel.
Every now and then I have to add a column for some interesting information I'd like to store. That's way more easy in Excel. If you have implemented a nice interface in Access and have to add something to the DB you'll have to spend some hours rebuilding the interface.
Before spending hours to list every domain in Excel you must think about what kind of information you are interested in saving:
Domain ID
Domain
Extension
Expires
Registrar
User name
Password
Hand reg/Drop/Buy
Money spent buying/regging
Money spent renewing
Money spent marketing
Sold?
Money received when sold
Offer received
Offer received from?
When bought?
Parked/Site/whatever it resolves
Parking income/Adsense income
...and so on...
Most important is: learn how to use excel! how to sort lists, how to do a search, how to replace, how to add together text, how to split text, how to make macros..
Make yourself a sheet for Adm. Total spent on domains, a total of .com domains, total of .net domains and so on, a total of income, net income.
I'm keeping track of app. 1.600 domains in my excel sheet and everything runs smoothly! :tu:
Make backups!!!
I also keep a print of all my account user names/password just in case I pass away, ends up in a hospital or whatever.

I also have listed contact information for some of my "online domain brothers" in the region. Just so my relatives can pay for renewals, sell my domains and/or get some advices from someone inside the business.