God planted a garden in Eden (Genesis 2:8). Why is it called Eden?
I don't see that any of the commentaries in my mikraos g'dolos discuss this.
R. Aryeh Kaplan's commentary on the verse (2:8), from The Living Torah, states that Eden means "Delight in Hebrew." The Meam Lo'ez (which Kaplan helped translate from the Ladino) explains that "the Torah informs us that God planted a delightful place in the east."
The latest edition of the Encyclopedia Judaica essentially states this as well. It discusses the derivations that DanF cites in his answer, but ultimately stresses this:
More likely is the connection with the Hebrew root ʿ dn, attested in such words as ma ʿ danim, "dainties," "luxury items" (Gen. 49:20; Lam. 4:5) ʿ ednah, "pleasure," (Gen. 18:12), ʿ adinah, "pampered woman" (Isa. 47:8); and in Old Aramaic m ʿ dn "provider of abundance," which would be a transparent etymology for the name of a divine garden. The Septuagint apparently derived Eden from ʿ dn, translating gan ʿ eden (Gen. 3:23–4) by ho paradeisos tēs truphēs, "the park of luxuries," whence English "paradise."
Traditionally, the favoured derivation of the name "Eden" was from the Akkadian edinnu, derived from a Sumerian word meaning "plain" or "steppe". Eden is now believed to be more closely related to an Aramaic root word meaning "fruitful, well-watered." The Hebrew term is translated "pleasure" in Sarah's secret saying in Genesis 18:12.
It's common for the Torah to use Aramaic words (we see many word imports in Breishit, esp.) The above explanation is credible.
Note: Sarah uses the fem. version עדנה . Rashi explains this word as deriving from something that "refines" the skin. I'm not sure how this definition related to the masc. definition.
Eden refers to pleasure as the Path of the Just writes:
"Our Sages of blessed memory have taught us that man was created for the sole purpose of rejoicing in God and deriving pleasure from the splendor of His Presence; for this is true joy and the greatest of pleasures (Edens) that can be found"