Pre-buying your tours of Athens, Greece can save you big money by avoiding the fluctuating Euro exchange rates. Here's a selection of tours worth taking. I've provided an on-line affiliate booking link for each, but similar tours are available in Greece through many travel agencies, hotels, and tour operators.
Taking a tour at the beginning of your stay in Athens helps orient you to the capital city of Greece. This one gets you to and from many of the major sights easily in a short amount of time; some you may want to revisit on your own later in your stay.
Cape Sounion is a dramatic location at any time of day, but most of the afternoon tours schedule it so you'll be there for the amazing sunset. Beneath you the Aegean Sea stretches out, glimmering in the sun; beside you stand the stately ruins of the Temple of Poseidon. It's easy to understand why the ancient Greeks built a temple to the god of the sea here.
Cliché phobic? Independent traveler rather than a tourist? Then this one isn't for you. You get to see the lights of Athens, look at the picturesque harbors, and then go into the Plaka area of Athens for a pre-canned dinner and show. Yet it's mindless fun, less trouble for a tired tourist than finding a unique place on your own, and nearly an essential experience for a first-time visitor to Greece.
Organized trips to Meteora make great sense - it's a long drive into the mountains that most casual travelers won't undertake on their own. This one includes a stop at Delphi as well.
Personally, I think a visit to Delphi is as essential as a visit to Athens. This beautiful, historic, and inspiring town on the slopes of Mount Parnassus is a great experience. Have extra time? You can turn it into an overnight trip and, with an early call, you can explore the site without the crowds early the next morning.
This is the version I recommend if you have time. Delphi is lovely and you won't regret spending a night there. Delphi is high on the list for a return visit by repeat travelers to Greece, and it is lovely almost any season of the year.
Frankly, I could give up the actual "Corinth Canal" portion of this tour. But the ruins of ancient Corinth are very evocative, both as an ancient Greek site and also as a site important to early Christianity; the "Bema" or meeting area where Paul preached can still be visited.
Tours too expensive or don't work with your schedule? Keep an eye out for the signs for the "Tourist Bus 400" - a hop-on, hop-off bus that costs just 5 Euro per day and goes to the major attractions in Athens. Sometimes it's even narrated. Caveats - the buses can fill up and you may be left waiting at a stop for some time, and it operates only during "Tourist Season", approximately April into October, but you can't beat the price. It won't take the place of an in-depth tour, but if you like public transport and being independent, it may be perfect for you. Grab a pamphlet at the airport - most hotels help keep this one a secret.
