• "We don't see things as they are, we see things as we are." ~Anaïs Nin
• "Learn the rules so you know how to break them properly." ~Dalai Lama
• "This is not a clue...or is it?" ~Bart Simpson
• Summary: the format of the clue is often as important as its content
• There are many kinds of clues, and meanings of words
• Be prepared to think both literally and metaphorically -- and outside the box(es)
• HSW 5: Carefully Consider Clues with Question Marks (?) (and other punctuation)
• HSW 9: Pay Attention to Foreign-language Answers
• HSW 3: Keep in Mind Multiple Meanings of Words
• about.com: 3. Clues Obey Rules; 6. Constructors Love Confusion; 7. Wordplay is Wonderful!
• Word Buff: 2. Become Familiar with Cluing Conventions
• Wonder 1. Use Grammatical Indicators; 2. Break Down the Clue's Structure
• Wikipedia: Crossword: types of clues: consistency; non-dictionary words; themes; indirect clues; cryptics; double-clue lists
• Anatomy of a Crossword Clue: Abbrev.; Partials; Capitalization; Agreement; Wordplay
• Exploring the history and rules of crossword puzzles 11/2/2010
• Become a Crossword Super Solver by Will Johnston Rules for clues; Varieties of clues; [.pdf; p4]; 1/19/2010
• NYT: Clueless (Editor do make errors; Constructors sometimes break 'the rules'); 8/19/2001
• BarelyBad: Relationships between clue and answer: Equivalence; Commonality; Set membership; Fill in the blank (FITB); Analogy
• Clever Clue of the Month
• Saturday Stumper (Newsday) Solving Hints;
  What Makes the Stumpers Tough?
• Example (NYT 1/23/2011) puzzle(blank): [.pdf]; solution: [.pdf] neat, [.pdf] handwritten
• FITB (Fill In The Blank): 32-A, 36-A, 79-A, 85-A (!), 97-A, 128-A, 2-D, 9-D, 11-D, 41-D, 87-D, 95-D*, 121-D
• first name: 1-A, 39-A, 65-A, 67-A, 96-A, 101-A, 118-A, 8-D, 66-D ('familiarly'), 116-D
• last name: 24-A, 89-A, 5-D, 9-D, 58-D
• *-prefix (theme answers): 6-A, 12-A, 17-A, ...
• plurals: 22-A, 47-D ('they'); 42-A&45-A (repetition); 61-A ('and the like'); 8-D ('and others'); 37-D ('array');
  28-D, 81-D, 86-D ('?'); 31-A, 46-A, 59-A, 71-A, 124-A, 1-D, 3-D, 16-D, 27-D, 33-D, 46-D, 60-D ('-s')
• abbrev./acronym: 28-A ('briefly'), 100-A ('Vette); 105-A, 70-D, 85-D ('org.'); 10-D ('sch.'); 23-D ('Trig'); 33-D ('R.N.s'); 81-D ('letters'); 96-D ('acronym'); 112-D ('abbr.'); 82-A, 94-D (?)
• singular: ('when repeated'); prefix: 74-A, 114-A; tense: 50-A ('-ed'), 35-D ('took'), 99-D ('-ing')
• adverb/adjective: 18-A, 126-A, 21-D, 51-D, 78-D, 79-D, 105-D
• literal: 22-A(año), 42-A & 45-A ('N N N'); refs to other clues: 61-A
• pop culture/music: 1-A, 24-A, 26-A, 29-A, 36-A, 39-A, 65-A, 67-A, 88-A, 96-A, 101-A, 122-A, 127-A, 8-D, 9-D, 13-D, 38-D, 40-D, 42-D, 54-D, 66-D, 73-D, 77-D, 92-D, 116-D, 117-D
• literary (2 Shakespeare!): 32-A, 2-D, 5-D, 52-D; slang/current: 38-A, 85-A, 104-A, 7-D, 92-D, 109-D
• geographical/historical/political: 12-A, 29-A, 89-A, 118-A, 9-D, 14-D, 68-D, 70-D, 87-D, 102-D
• math/science: 12-A, 23-D, 58-D, 64-D, 87-D, 111-D
• crosswordese: 62-A ('as is'?), 96-A ('Ara'), 28-D ('A-one')
• languages: Spanish: 30-A, 63-A; French: 59-A, 103-A; Greek: 42-A; Latin: 86-D; (?): 93-A ('whence the word')
• Roman numerals: 78-A
• compass heading: 48-D
• puns: 76-A ('carrying a toon')
• ambiguity: 31-A ('winds'), 34-A ('touch'), 49-A ('slant'), 68-A ('hood'), 69-A ('shocker'), 90-A ('King'), 98-A ('Numbers'), 116-A ('don't get it'), 114-A ('opening'), 124-A ('homes'), 125-A ('house'), 1-D ('heads'), 6-D ('party'), 15-D ('in a way'), 12-D & 16-D ('pointer(s)'), 28-D ('tops'), 32-D ('prone'), 43-D ('hitch'), 47-D ('keys'), 57-D ('opening'), 81-D ('letters'), 106-D ('bit'), 115-D ('revealing'), 119-D ('straight')

A few other "interesting" examples I've collected:

• reference to letters/sounds. RV Center: STU; Head of cattle?: HARD C; Carriage part?: SILENT I; Workweek sequence: Abbr.: MTWTF; Alphabetic pentad: AEIOU; Queue after Q: RST; Tic-tac-toe win: OOO
• music. Like Bach's second violin concerto: IN E; A flat equivalent: G SHARP; musical key: 'A-G' [MAJOR | MINOR]; It's probably played first: SIDE A; Score keeper?: MUSIC STAND
• people. Happy cohort?: SNEEZY; Bird, e.g., once: CELT
• directions: U-turn from WNW: ESE; Needle point?: ENE
• Lion's home: DETROIT
• Last picture in an alphabet book: ZEBRA
• Response to a general question?: NO SIR
• Stirring time?: SUNRISE
• Something played out in a theater: WAR
• Departure info?: OBIT
• Stayed out?: SLEPT
• Gambler's opening: SLOT
• Iron-deficient?: CREASED
• Polar opposites?: NAUGHTY OR NICE
• Cold capital: OSLO
• Pique condition?: IRE
• Time before the present day?: CHRISTMAS EVE
• #10 on a table: NEON
• Flat sign: TO LET
• Where cells are of little use: DEAD SPOTS
• Something you can bank on: POOL TABLE
• "Stop! You've got it all wrong!": NO NO NO
• It may have you in an awkward position: YOGA CLASS
• Definitely not a company man?: HERMIT
• Rolling stone?: LAVA
• Secretive group?: GLANDS
• Army heads: LATRINES
• Can of Newcastle: LOO
• John, to Paul, George or Ringo: LOO
• M.A seeker's test: GRE
• Geometric suffix: OID
• French, e.g., Three, in Tours: TRE; Part of l'été: AOUT; Stop on the Métro?: ARRET; Like many squares in a French crossword: BLANC; Security Council veto: NON; Feu fighter: EAU
• Spanish: New Mexican: NENE; Enero begins it: ANO; Mayo is in it: ANO; "Keep them coming, Juan!": MAS; Spanish she-bear: OSA; Bit of change in Cuba: CENTAVO
• Latin/Roman: Uncommon in ancient Rome: RARA; One quarter of M: CCL; Nvmber of bones in the human body: CCVI; When Othello kills himself: ACT V
• literal references to patterns in grid, direction of clue (ACROSS | DOWN), ...