What kind of tripod would you recommend for macro photography? The subjects being flowers low on the ground. I have a fairly good tripod but the center column gets in the the way meaning that I can't lower the camera enough.
With this tripod, I can place the camera upside down. Sorry for asking but is this an usual macro photography way of shooting? My setup consist of a T2i, extension tubes, focusing rails and external live view remote.
Well, I'm not sure what you mean by 'with this tripod, I can place the camera upside down' - but many existing tripods can invert their center post and allow you to place the camera between the legs of the tripod. This may or may not be sufficient for what you're asking, its difficult to tell without seeing your setup.
Other options may include a tripod like the Manfrotto 055XPROB which has a center post that can rotate and tilt over its legs (see the picture on the included link). This would allow you to get closer to your subject if the other method doesn't work.
Look at Uniloc or Benbo tripods - capable of placing your camera in almost any position.
You might have just a fine tripod. Perhaps a clamp on the tripod leg with another head on it will do the trick. I have a nice heavy tripod that I use this way and it's pretty much the only way to get right down to the ground. The tripods with columns that can be placed transversely across the top or canted out are good if you are shooting down, but you have to counter-balance them.
This is generally what you need for a tripod leg clamp. It's set up as lighting gear, so you'll have to figure out a way to mount a ball head to it, but then you're ready to go.
A Gitzo Explorer or similar tripod works very well for low-to-the-ground macro photography. All three legs adjust to different angles independently, as does the center column. You can position the camera a few inches off the ground, and you don't need to worry about setting up on a flat surface. Gitzo makes a number of Explorer models, and there are some Asian knock-offs such as Benro that are less expensive and may work just as well.
You also should consider a ball head with versatile positioning. It's one thing to position the camera low to the ground, and another to do so with the camera at the proper angle, and to be able to adjust the camera angle without having to reposition the tripod legs and column. The Gitzo ball head mentioned in the previous link seems to have a lot of degrees of freedom. Other options would be a ball head with multiple drop notches, such as those made by Really Right Stuff.
I have the Vanguard Alta Pro 284 CT which has an inclinable center column and can really recommend it. The cool thing about this tripods' center column is that you can set it up from zero to 180-degree angle. I've put a ball-head which is -100°/+40° tilt capable on it (Manfrotto 054 Mag Ballhead). Adding a L-Plate (i use a DIY) i can take any position and angle I like.
In addition to @rfusca's recommendation on the 055XProB, note that you may find a 3021BPro either new or used. This is the older version with essentially the same capabilities of reversing the center column or mounting it horizontally, for vertical shots.
Also note that you can purchase a short center column replacement that will let you lower the tripod to a very low position with the camera mounted straight.
