Can anyone tell me if they've had much luck with either of these products - Toppik and Nanogen - or anything I should be aware of? I've just learned they exist and they sound great (I have a thinning crown only). Or if there is another product that is easy and undetectable, and actually covers the scalp. Thanks.

Toppik is awesome for the crown. And it's cheap too so you don't risk much by trying it.

Toppik is great, especially for the crown--it is undetectable. I use Covre (also sold by the Toppik company) first, then apply Toppik. Both products are reasonably priced. If you are trying to thicken your hair, try Suave Professionals volumizing shampoo--it's cheap and works really well. Also, Aqua Net hairspray will keep the Toppik in place. The Suave and Aqua Net can be bought at Wal-mart or any other store.