I've been spending a lot of time at the Trading Card Database. The site has complete checklists for just about every set ever made. Variations and inserts are included too. Registering for the site gives you the chance to check off on their lists the cards that you own.
Last weekend was a four-day weekend, so I spent parts of most of the days entering most of my collection into the site. As of yesterday, I have 101,596 cards cataloged.
That is just what I have up to 2017. I'll be spending time over the next few days finishing up with my cards up to 2020. My number isn't quite accurate, though, with my Topps Cubs cards. I have two of each Topps Cubs base card from 1969 to 2020, one card in the complete set and one in the Cubs binder. But only one card is logged into the Database list. The same is true with Fleer and Allen & Ginter, since I have complete sets for each year of those brands.
I also like that the TCDB has pictures of many of the cards. I can also do a search and find which cards I've entered do not have a picture in the database. In the future I plan to upload mine to the site.
I will still maintain my Excel sheet of my collection. The Trading Card Database will be a nice backup.