As others have said, it pretty much depends on the matieral of the toy.
If it is a jelly toy then you're not going to get rid of the smell. The jelly is made up of chemical compounds, these are breaking up which releases the smell. Eventually the jelly will break down all together. I.e the toy will get tacky, and begin to melt; regardless of how well it is cleaned after/before use.
The same can happen with rubber toys too.
I would suggest getting toys made from non porous materials, such as silicone, glass, metal. Yes these toys are generally slightly more expensive than the jelly, however with proper care they can last a life time, they can be steralised and you won't get that awful smell.
Lovehoney actually has quite a few of their own branded silicone dildos which are priced decently. x