The Greek festival is at St Theodore's on Cipriano Rd, off Greenbelt Rd/Rte 193 (near Goddard Space Ctr - turn at the K-Mart) All-day this Fri-Sun.
Terrific food as usual, and wonderful live music & dancing Fri. & Sat. nights. In the past, I've found the food here slightly cheaper than the Greek church fests on Bradley Blvd in Bethesda, & at 36th & Mass. in DC.
The Taste of SS (Saturday only, 12-6) is new to me, so I can't vouch for its affordability or quality. It may be the 1st or 2nd one that's been held in downtown SS. I gather it's somewhere between the $1 bargains at the Taste of Wheaton, and the way over-priced bite-sized samples of the Tastes of DC & Bethesda. There is also live music & entertainment.