There a good, inexpensive macro lens/adapter for my Digital Rebel?

I have a Canon EOS Digital Rebel with the standard 18-55 lens and a 75-300 lens I got in December. They're good lenses (the zoom lens' auto focus has let me down a few times, but I've got it on MF now) but I'm really interested in playing with macro photography too. The other lenses are great for birds and flowers (mostly) but for insects and other small, pretty things, they can't cut it. So I'm wondering if anyone's had any experience with the macro adapters I've seen all over eBay for my camera? Is there something better out there for me? I don't want to spend a truck-load of money, but I don't want to spend anything on something that's going to disappoint me, either.

Any guidance on choosing a lens or adapter would be greatly appreciated. Thank you.

There are a couple of ways to do it. I'm not familiar with Canon specifically, but the two least expensive ways to get some decent results would be:

Extension Tube - simply a tube that goes between the lens and the camera so that it will focus much closer. They come in different lengths, and sometimes sets. They won't have any optics, so there's nothing in the optical path to degrade the quality of the image.

Close up lens/filter/diopter - screws onto the front of the lens like a filter, and will allow the same result (closer focusing). Best to get one quality lens (like Canon or B+W brand) rather than an inexpensive set.

Both are easy to carry and use. I've used both but had limited experience with them. Not really sure which one to recommend, but I'd probably go with the tube because it's simple - as long as it allows for automatic metering with the camera. You will probably have to manually focus, but that's best anyway with this type of photography. With tubes, you don't need to necessarily stick with the Canon brand - Kenko makes good ones (same company as Tokina lenses).

Ah, those look like they'd be alright. Hopefully they aren't too limiting, but I guess they're the best option short of buying a macro-specific lens.

Thanks. I'll browse around eBay for some.

The longer the tube (or more powerful the diopter in a close-up lens), the closer you can focus. A short tube (8-12mm) will still give you a ton more macro capability than you have now, so I'd probably start with one of those.

They can also be used with long lenses to get it to focus inside the Minimum Focusing Distance, but not exactly macro situations. For example, you could probably focus your 300mm lens at 2-3'. That would give you a very different perspective than how we see the world every day.