Is there a good method of checking sale prices on items online?

I once stumbled across an incredible sale at Best Buy on my favorite video game series. I didn’t have the cash available, so I didn’t get anything. I got 150$ in gift certificates to Amazon so I was going to buy from there.

I didn’t want to buy unless I found a better deal than was on sale at Best Buy all those months back, so I’d just randomly check Amazon every other week or so. Well two days ago, I got amazingly lucky. The games I wanted were 66% off. I bought around 120$ worth of games for under 50 bucks. I told some people about it, but the next day, the sale was gone! I got REALLY lucky. There were only 2 items I wanted that I didn’t get because they weren’t on sale. One was only on sale for PC but not for Mac, and the other was a brand new title that of course is still full price.

Anyway, is there a good way to keep an eye out for sales on items you want that doesn’t involve obsessively checking websites every day? I’d also request leaving Ebay and other resellers out of the picture because I don’t like to buy software on ebay. I’ve had mixed results (like the seller not mentioning that they were selling the UK version of software and it wouldn’t work with the US software already installed.)