I need appetizer ideas for friends' dinner, main course is Greek swordfish, thanks!

If you have the book Jerusalem, the pureed beets with yogurt, while not Greek, is totally delicious and would be complementary. I made some pita chips with whole wheat pitas and also served carrot sticks for those who don't eat pita. If you don't have the book, the recipe is also available through Food & Wine, but it is a little different than in the book.

Thank you so much everyone! So many ideas to choose from, I really appreciate them all ;)

Really good olives are good beginning. And they don't even have to be greek olives---castelvetranos from southern Italy or luques or picholines from from France. You can seriously tart them up with white anchovis. Honestly I am not a big fan of kalamatas. Usually they don't taste like anything other than olive pulp.

Whenever I do a Greek themed dinner I like to serve an antipasto platter of tomatoes, cucumbers, red onion, kalamata olives, feta cheese, kasseri cheese and tarama (Krinos makes a decent one already prepared ). And some great greek bread! Here's a photo with some calamari thrown in.

Just saw this and can't help adding it. You'd of course cut the flatbread into finger-sized pieces for an appetizer. I might swap the 2/3 cup sultanas (golden raisins) for 1/3 cup golden raisins and 1/3 cup capers without juice.
Grilled Fennel Flatbread with Olives and Sultanas
http://food52.com/recipes/16929-grilled-fennel-flatbread-with-olives-and-sultanas

OK, that's it! I've been killing some time waiting for a call. I won't bombard you any more!

If your area is still inundated with tomatoes:
Bruschetta with tomatoes, capers, onion, feta, oregano, dill
NY Times, Martha Rose Shulman
http://www.nytimes.com/2010/08/26/health/nutrition/26recipehealth.html

White bean (cannellini) and sundried tomato dip for crackers / crudites:
http://food52.com/recipes/2368-white-bean-sundried-tomato-dip

Or... Fig and Olive Tapenade:
http://food52.com/recipes/8844-fig-and-olive-tapenade

It's not Greek but would be a nice Mediterranean companion to the swordfish: eggplant caponata on toasted bread rounds. There are several recipes for caponata on this site but here's one:
http://food52.com/recipes/21728-silky-sweet-sour-eggplant-caponata

If you have time, for a nice garnish: halve some cherry tomatoes and gently squeeze out the seeds and pulp. Smoosh a little goat cheese into each cherry tomato half. Spread the caponata on the toasted bread slices and place a stuffed cherry tomato on top of each toast for garnish.