PC-Decrapifier is a great one to run on newly bought systems, but most of us will probably know what they want to keep on a new system.
I must admit I really like Auslogics and have many times considered buying BoostSpeed, but I always come back to; Do I really need to pay for that small extra ?
(of course there are other ways, but those imply you trust the source of those other ways.. I never do..)
Also, I really like having Process Explorer run at startup on all the PCs I manage, with very little explanation to users, you can tell them how to check which process is using resources which can help you help them when you get that dreaded phone call ;
"Dude, my PC seems slow.."