A Sunny fan I see....
A lot of people will use regular tap water but that's a mistake, smart people will upgrade to IceBastard branded Ice which is a good choice. But IMO ice made using Fiji water is the best I've found so far. It's a bit more specialized and expensive but it just can't be beat. It tastes so much better and makes your soft drink taste better too (not saying that IceBastard isn't already good high quality). Just don't reuse your Ice, it will make your soft drink taste off and the backwash that gets on it while in another drink will scratch up the inner lining of your straw.
Either that or Whiskey rocks that have been put into your freezer for a while (you can reuse these if you wash them). http://www.teroforma.com/Set_of_9_Wh...nes_20187.html
I don't recommend it for most soft drinks though, it's very specialized, I don't even use them. Most people will settle with either Fiji water ice at most. I personally use IceBastard Ice.