Life-size converters
For macrophotography, besides a macrolens, a set of life-size converters is very useful. With life-size converters you can usually easily reach life size (1:1 reproduction ratio) even without a macrolens. I use life-size converters in combination with my EF 70-300 IS USM or EF 100-400 IS USM lens. This gives me the opportunity to take photo's at longer distance from the subject than possible with my macrolens. Life-size converters are manufactured by several compagnies. Since life-size converters do not contain any glass (it is actually an empty 'shell' that places the lens further away from the camerabody, but keeps the communication between the camerabody and the lens intact), it doesn't really matter which compagny produced the life-size converter.
Accessories
Flashes
I don't use I flash very often. I own a Canon Speedlite 430EX II. It works very well. This flash has a flashhead which can rotate horizontally and vertically, so I can also flash straight-up. The 430EX II also has E-TTL and highspeed flashsynchronisation. For me it's a very good flash for those moments I need one, since I rather don't use it. Moreover: usually I use a 'difusor'. This is a plastic cap that is placed over the flashhead so the light is getting diverted. Similar as if you flash through a bulb. The effect is usually a smoother picture.
Trip- and Monopods
I use tri- and monopods, all made by Manfrotto. Beside a firm tripod with a ball head with quick-release (type: 055xPROB with 486RC2 ballhead), I use a monopod, also provided with a ball head (type: Manfrotto 676B Digi Monopod with the Manfrotto 484 mini Ball Head). The choice for a ball head on my tri- and monopod is because I have experienced that this works the best for me (simple and quick). When I travel I usually take a small tripod with me (Manfrotto 345-Table-kit), instead of the Manfrotto 055xPROB. Especially at citytrips, it's frequently not allowed to take a tripod with you into buildings (churches, museums, etc.) A table-kit is very useful in those cases and it is not so heavy.
Angle view finder
In landscape photographs a foreground is of great importance, so I usually take my landscape pictures close to the ground. By using an angle view finder, it is not necessary to lie down on the ground every time. It makes photography more enjoyable. In addition, my angle view finder has a zoom option, which is great doing macro photography.
Remote controle
If you need a tripod for making a photograph, then a remote control cannot be lacking. I use the Canon RS-80N3, which can be connected to the camera with a cable. With a remote control it is also possible to make so-called ' Bulb-shots'. This means the remote control helps you in keeping the shutter opened for a longer period of time. Very usefull for nightshots.
Cases
When I go out to make pictures I use a Lowe Pro Fastpack 250 or Lowe Pro Compurover AW backpack. I Use the Fastpack when I only need my camera with standard lens, a flash and a wideangle lens. The upper compartment of the bag provides space for food and drinks. The advantage of the Fastpack is you don't have to take off the backpack to get to your gear (like the Slingshot series the backpack has a side-access). The Compurover fits the camera, all lenses, other camera accessories like life-size converters, remote controles, grey filters, etc., a coat, food and drinks. When needed it is also possiblle to bring my notebook. If you put the backpack down, you can rapidly and easily take out your equipment. If I only want to take the camera with me, I use a Lowepro Topload Zoom case (fits the camerabody, including batterygrip and my standard-lens). In those cases I use Lowepro-lenscases for my telelens and wide-angle lens.
Raincover
It's not always dry-season. And because I want to have the option to take pictures anytime and anywhere I sometimes use a rain cover (trademark Matin). Except the fact that this cover is impermeable, it is also conducted, as a result of which the camera is also protected against getting damaged or the cold, as well as my fingers.
Imagetank
When you travel and you take a lot of pictures, you will easily find yourself in the position that you'll need a lot of memorycards. At least, I do, since I useally don't bring a notebook. For this reason I have bought an other portable medium to store lots of photo's: an image tank. Besides the fact that an image tank reads Compact flashcards directly (you put the card partly in the tank), there are models on which you can watch the photographs when the copying proces has finished. Some image tanks can also play MP3's and movie files. Image tanks are available in several GB capacities. I use an Epson image tank (the P-3000) which has a capacity of 40GB.