First of all, Imageshack is not an upload site as you already know.
You're probably asking for an image hoster. And for the time being I can put PicTiger on the table for an alternative. TinyPic.com has a 250k limit if I'm not wrong, though may be useful sometimes.
If you're looking for free upload websites, there are a bunch of them -despite it is hard to figure out which one is fast and/or reliable. Rapidshare.de , MegaUpload.com are the first ones I can come up with right now. Hope this helps.
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