I'll 2nd what most have said, and add my $.02.
Syncline area sounds right up your alley for tech, there are a bunch of trails that make smallish loops: Little Moab, Coyote Canyon, Hidden Valley, Wizard all have fun tech spots. Make a day of it, ride for a couple hours in the morning, go eat, ride the rest after lunch (or go hit something else nearby like whoopde).
St. Helens has the most beautiful scenic (and fun) rides, Lewis River, Siouxon, Ape Canyon/Plains, Falls Cr. You'll be doing yourself an injustice if you don't ride at least one of those.
Mt. Hood is mostly set for ripping burms, but still lots of fun. 15mile and Dog River are about the only things that come to mind with a little tech there. Surveyor's is beautiful and worth a ride though.
Blackrock and Post Canyon have the best freeride around.
On my secondary choices list:
Both Larch Mts (OR/WA), are fun. GT400, Scappoose, Browns/Gales, Tarbell have fun tech spots and these are all the closest to town (depending on what part of town your in)...
If you have time to get down to Oakridge it is impressive to see what a community of bikers can do. Waldo, Alpine, Larison, Middle Fork are all good.
If you are going to make a trip out of it Mckenzie or North Umpqua are amazing.
Damn I've got myself all worked up now just thinking about it...
Have fun. Post when you'll be here, someone will be happy to show ya around.