I, too, have quite an oily t zone and find that it's exacerbated by layering foundations/primers that contain silicone. I've since discovered both Smashbox's Primer Water (silicone, oil and alcohol free) and the new Nars fusion type foundation which in combination leave me shine free for a good 6 hours. The Nars does contain silicone (in fusion with water) but gives a beautiful finish to the skin - matte but not flat. At a similar price point is the YSL fusion ink foundation which I also think is lovely, although its coverage is slightly sheerer and its finish a little less luminous.
Although I love face powder I do find that using it throughout the day over the t-zone can result in cake face, so I prefer to powder once only in the morning and then use blotting sheets throughout the rest of the day as and when needed.
I've not tried the new Bourjois one, but I'm on my second pot of their unifying powder which I love, and this having tried every powder known to man, including Suqqu (which I also love), Clarins, By Terry and even the ridiculously expensive Chatacaille HD powder (nothing but posh chalk). The Bourjois unifying powder is extremely good quality and relatively cheap, too.
The other tips I've found useful are as follows:
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blot directly before and after foundation application. This takes off any oily residue from serums/moisturisers, plus that from your foundation, leaving only pigment. Then powder lightly on the t-zone only.
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Make sure your skin is not dehydrated (as opposed to dry). If it is it can end up producing more sebum on the t-zone to compensate.
I've also tried the MAC blot powder which is great but rather too large and too expensive for what it is. I found these on ebay after reading fantastic reviews. They're smaller and cheaper, but do the exact same job, so are purse friendly in every respect!
Hope this rather long-winded reply helps!