it really depends on your traffic source/type. there are e-mail submit's for just about any-and everything nowadays, and if not most am's will try there hardest to have one made for you if you need it. if you want more specific suggestions you need to provide a bit more information as to what you're looking for because some networks will have 500+ email submits alone. But in general you can either ask your am or look at the offers information to see what does best on your network, most of them list the "epc/rpc" (earnings/rate per click) so you could look there as well.