At the end of Rambam Hilchot Avodah Zara 5 (halacha 14 by some counts, 10 by others), he says
ואפילו להזכיר שם עבודה זרה שלא דרך שבועה--אסור, שנאמר "לא תזכירו". לא יאמר אדם לחברו, שמור לי בצד עבודה זרה פלונית וכיוצא בזה. וכל עבודה זרה הכתובה בכתבי הקודש--מותר להזכיר שמה, כגון פעור ובל ונבו וגד וכיוצא בהן.
Basically, it's forbidden to mention the names of idols, even to say "near idol x", except for the ones mentioned in Tanach.
As far as i know, the Greek gods are not mentioned by name in Tanach (see Are any Greek or Roman gods mentioned by name in the Bible? on Christianity.SE, which mentions a couple from the NT but none from Tanach).
However, i know Orthodox Jews who indeed mention the names of Greek gods.
Is there a heter for this practice? Perhaps because they have entered Western culture (unlikely though, because idolatry was big in Eastern culture as well, and is clearly forbidden ;)). Perhaps because they have fallen out of favor for the most part? (Though see Does anyone still worship ancient greek [sic] gods like Apollo and Diana? on Yahoo Answers, which says that there are.)