The best basic config would be to go to apple's site and order the default 8-core with the 4870 graphics. Get a 250Gb OCZ SSD. If you capture use a Phoenix for SDI/HD-SDI or an LFG4 for Composite.

You could honestly get away with the 4-core machine if you wanted however the 8-core is easy enough. You don't need anything more on memory or anything else.