The hardware you want to get kinda depends on the mounts that you have.
The vark bar is a good starting point...
http://www.posthorn.com/Macvk_4.htmlThen there's the popular Shure vert bar...
http://www.shure.com/ProAudio/Products/Accessories/us_pro_A27M_contentLots of people enjoy using the AKG mounting bar...
http://www.fullcompass.com/product/299818.htmlAnd I've used this Sabra Som bar with plenty of success.
http://www.sabra-som.com/detalhe_produto.php?pag=p&cod_prod=ST2&lang=3All of these are good starting points, but the first two provide the added benefit of giving a vertical offset so that you can mount your mics in X-Y coincident. On the other two mounts, you need to improvise a little bit in order to get the mics offset. With the sabra-som, I found a 2 inch adapter at the local guitar center with 5/8in female on one end and 5/8 inch male on the other.
Note that you mention that some have complained about the Shure mount. You ability to get true 17, 20, and 30 cm spacing is as much a function of your mounts and mic size as it is the hardware. There's no 'one size fits all' hardware solution. If there was, then everyone would buy that one solution.
So what you need to do is buy something that is most versatile for your needs and figure out what will give you the most options for providing the exact spacing required. The people that bitch about the Shure bar most likely just don't have shock mounts that are adjustable enough to give them the spacing they need/desire. IMHO, this isn't a function of the Shure bar being a poor design, as much as it is a function of poor knowledge or advance planning that the people have that the hardware will put their mics in the proper configuration.
I also have the Shure vert bar and I think it rocks...but there are times when it's just not the right mount for a specific setup.
Hope this helps.
Steve