Cut-off wheels I use Metabo Super Slicers...last longer than the other ones I've used and I buy them by the 50 pack
Flap wheels I like Norton wheels. They hold up longer...of course, select the grit based on how much you have to take off.
For grinding wheels I like the Nortons as well...Gemini Type 27s...again, select the grit based on how much you are going to need to remove.
I buy pretty much everything like this in bulk, usually 50 or 200 packs depending on the type of wheel, grit, etc... and how much I'll need to use that particular type. I don't really qualify as your general DIY in your garage though since I'm probably burning through around $200 in consumables a month on just my welders.
Ohh, and for grinders, I have three Dewalt D28402's 4 1/2", two of their older 4 1/2" models, a Makita 7" and a Dewalt D28494N 9".
"No man's knowledge here can go beyond his experience." - John Locke
"Vi Et Armis" - Cicero