Down below gives you a rough idea of what your looking at. For tri SLI I would look at a 1200w - 1500w psu. But again it's too early seeing how you don't plan on buying for awhile from now. That mobo down below is spendy...like real expensive but if you were to do tri sli that's the one I would recommend. That board runs dual cards @ 16x and tri cards @ 8x. There again I would never run tri SLI seeing how the gains are small for what you pay. Dual vid cards seems like the way to go imo.
Approximate Purchase Date: End of the year (rough idea type stuff)
Since peeps been waiting this long for the top end i suggest for healthier/fatter budgets to
1. Await Z68 chipsets, Zambezi AM3+ on platform front
2. Await HD 6990/GTX 590 on the GPU front and price revisions
3. Await the Sandforce SATA 6GB/s SSDs to hit retailers