It's a big list - lots of countries, denominations, and SILVER fineness to consider. In addition, condition of the coins has some importance as old worn coins can lose as much as 10% of their weight due to wear. Start with the popular countries, like Mexico and Australia for some good deals. Australia will be easy, SILVEery coins 1945 and older will be ALL sterling (92.5% fine); know the ASW of every denomination (3 pence, 6 pence (half a shilling), shilling (half a florin), and florin (.3363 ASW); crowns go much higher than melt) so you know what the coins are worth. GB coins before 1920 are sterling (same fineness and denominations as Australia), 1920-1945 are 50% SILVER (florins contain .1818 ASW, other denominations pro-rata), after that mostly copper-nickel. Mexico is all over the place, but the dollar sized pesos dated 1920-1945 (72% fine) contain .3856 ASW have $10.30 melt value each. A recent favorite of mine is Netherlands 1G (1954-1967, 72% fine, .1504 ASW) and 2.5G (1959-1966, 72% fine, .3472 ASW) - a little obscure, but nice sized SILVER European coins with little wear that may be missed by many dealers.
I would suggest buying an old Krause coin catalog for $10 or less and take it with you. Once you can recognize the SILVER coins (don't assume that the coin is SILVER just cause it's marked so on the 2x2), you can look up the ASW in the book, multiply it by the SILVER spot, and know the melt value of the coin. You want to pay less than melt for these foreign coins. Dealers will sell them for melt or higher (unless of course YOU know your coins and buy it cheap from him), but will buy them for less. Other folks will be looking to get a good deal from you when you sell the foreign SILVER. So, try to buy at a large discount from melt from those who would sell to you.
Hope this helps a little....