1. You can use the promoter of vir genes like- virA, virB, virC, virD, virE, virG.....The following report may help you..(http://www.ncbi.nlm.nih.gov/pmc/articles/PMC339509/pdf/nar00272-0225.pdf)

2. Otherwise you can use mannopine synthase promoter. following report may help..

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC557759/

http://www.pnas.org/content/86/9/3219.full.pdf

If you need expression of a protein in Agrobacterium tumefaciens cells, nos promoter seems to be not the best choice because this is the plant-type promoter transferred as a part of T-DNA into plant cell for further integration into plant genome and supporting opine synthesis in plant cells. For bacterial expression you should better choose some promoters of opine catabolism (they are opine regulated and might be strain specific)

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC205073/

http://link.springer.com/article/10.1007%2FBF00290241#page-1

Otherwise using of common lac promoter  was shown to be effective for Agrobacterium cells

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC207234/?page=3

I would agree with Yuriy comment, eventhough Nopaline syntase (nos) gene come from Agrobacterium, it is not necessarily actively express in the bacterium. The nos gene is a eucaryotic gene and the nos promoter will actively transcribe transcription unit in the eucaryotic cells (i.e. plants). That is why the Agrobacterium need to transfer the nos gene into plant cell to synthesize nopaline.

Unless you have specific objective to specifically express the protein in Agrobactecterium, for protein expression in bacteria - I would not use Agrobacterium but use standard bacterial expression strain commercially available. It already has a number of appropriate promoters for expression purposes.

I hope I am not mistaken about the question and given the wrong answer. Good luck...

Thank you very much to Kutubuddin, Yuriy and Sudarsono for their interesting answers. Sudarsono you got it right, I want to test promoter activity and related protein expression directly in Agro cells. Using lac promoter seems promising, I could try that.

In fact I am just wondering... would an Agrobacterium promoter, not originally into T-DNA, be driving active protein expression in Agrobacterium cells if inserted inside T-DNA? 

I can only guess that the bacterial promoters, integrated in the T-DNA part of the Ti-plasmid, will be able to drive expression of a transcription unit in the bacterial cells. Unlike the plant genome, there should be no positional effects associated with where the promoter (or a gene) is integrated in bacterial plasmid (or chromosome). You can always try doing it your self or googling for it in the internet. Good luck...