i hate to say it, but there really is no substitution for fish sauce and your asian dishes won't be the same without it. do you like thai food? if you've ever had a thai curry and liked it, then don't be afraid to use the fish sauce b/c you undoubtedly have had it before if you've ever had thai!
fish sauce smells pretty bad but the smell goes away after cooking. don't let the initial smell put you off. also, don't be tempted to use it liberally - just use what is called for in the recipe.