Macro filters. I have never tried these, and can therefore not give a first hand review. But, the method is that you can attach a filter in front of your lens, and achieve some result. They work like magnifying glasses.
I have anyway chosen to add them to this list of ways to do macro photography, because they are available, and because they are fairly cheap.
Macro filters are graded in diopter, where +1 being less and +10 being more (closer focus). You can also stack the filters. When stacking, you should place the filter, with the highest number, closest to the lens.
With macro filters it can be harder to focus.

Information If you don't want to invest in a macro lens, then maybe this solution is right for you. On Amazon a set of macro filters can be found from £8.50. - This is the cheapest price I found, and it is only to give a clue at what the price level is at. Of all the methods explained here, I would though suggest the bellows before this. I have no first hand experience with this, I must admit though.

Foreword	Macro	Bellows	Extension tubes	Macro filters
Macro lenses	Reverse ring	LED ringflash	Sliderrail	Tripods
Barndoors	Beautydish	Light modifiers	Reflectors	Reflectors, std
Snoots	Homemade gel	Softboxes	Speedlight gels	Umbrellas
Umbrellas, white	Umbrellas, silver	Umbrellas, golden	Backgrounds	Cameras
My studio	Flashmeters	Night photography	Stands	Studio strobes
Macro flashes	Trigger systems	Printers