I can vouch for the non-IS Canon 100 mm macro too - I had one for five years, then switched to the IS version about a year ago. The IS version has a lot of nice features (amazing IS, significantly faster focusing, better focus limiter, marginally sharper, etc) but most of them don't matter for macro.
A really economical way to get started would be some extension tubes (still useful for a "proper" macro lens) or a reversed 50 mm lens (Google it if you don't know what I'm talking about).
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