Personally I like Weblio, it includes a lot of words and sample sentences on a huge range of subjects. You can also click the links to jump to other words you don't know (like the superjump feature on some denshi jisho).
Can be used for both kanji and term look-up. Works both as a pop-over dictionary for web browsing and by copying and pasting in terms.
Recommended Print Dictionaries
Kenkyusha's New Japanese-English Dictionary
Call Number: UM East Asian Reference ; PL679 .K4 2003
Kenkyusha has long been the standard (and preferred) dictionary for North American scholars working with Japanese. Please note that the most recent edition uses kana and not romaji - this is a big change.
Saito's Japanese-English Dictionary
Call Number: UM East Asian Reference / PL679 .S17 1999
This is a reprint of the original 1928 dictionary intended for Japanese readers who want to write/speak in good English. It does include sample sentences in Japanese but you must know how to read the kanji before you can look up the terms (kana order). Also, the English->Japanese concordance gives readings for the Japanese terms.