Miss Frizzle (from The Magic School Bus):I can't believe I haven't included Miss Frizzle on one of these lists yet, and it is past time for me to rectify the omission. As Pinterest has proven, there are many interpretations of the Miss Frizzle dress. For my money, however, I'd recommend a colorful shirtwaist dress with a full skirt and pictures related to elementary school subjects (think stars and planets, fruit, musical instruments and notes, or numbers). If you can't find a dress with a pattern or pictures you like, you can make your own or you can always decorate your own by using fabric paint or by attaching fabric cutouts. Be certain to wear loud, kooky jewelry (fun earrings, necklaces, and bracelets all work) and colorful, school-themed shoes. For extra authenticity, wear a short petticoat under your dress to help your skirt stand out, get a stuffed lizard to put on your shoulder (or get a friend to dress us as a lizard), carry around a small yellow school bus, and use Miss Frizzle's favorite catchphrase - "Take chances, make mistakes, get messy!"
Dorian Gray (from The Picture of Dorian Gray): Given the nature of Dorian Gray's character, there are a number of different ways you could go with this costume. For instance, you could dress like a young Victorian gentleman and carry around a portrait of yourself that is older and more sinister. You could also do half of your face as young, innocent Dorian and the other half of your face as old, evil Dorian (the picture in question). Or, if there are two of you, one of you could be young, dapper Dorian and the other one could be old, sinister Dorian (complete the look of old Dorian by having the person wear a frame like this couple did). Whatever you do, go with men's evening wear (even a tuxedo would work - they were around in the 1890s).
Peter Pan: The NBC musical event is coming in December, but you can be ahead of the curve by dressing as the boy who refuses to grow up. Depending on your resources (and how elaborate you want to go), you can make this as elaborate or as simple as you would like. The classic look is a green hat with a jaunty feather, a green tunic with rope belt, green tights, and green shoes, but you can make adjustments as needed. For instance, if the weather is chilly, feel free to forgo the tights and wear pants instead. A Beautiful Mess has some great pictures and suggestions for making your own tunic. If you have friends who also need costumes, they can dress up as the Lost Boys (think pajamas with a hodgepodge of accessories) or Tinkerbell (a sparkly short dress, wings, and a sassy attitude).
Anne Shirley (from Anne of Green Gables and many, many other books): Anne Shirley (or Anne of Green Gables as she is fondly called by her legions of fans) is a distinctive character, but there is some flexibility when it comes to her clothing. Although most people likely envision Anne as Megan Follows from Kevin Sullivan films, Anne goes through a number of changes, so an Anne costume can be as simple or as elaborate as you (and your wallet) would like. If you want something simple, you can wear a long, plain dress with a pinafore, stockings, sensible shoes, and a plain straw hat, as Anne does when we are first introduced to her in the film and the book (red hair in tight pigtail braids is a must). However, you could also wear Anne's white organdy dress from her White Sands performance or her gown with puffed sleeves (if you want to be true to the book, the dress should be brown and in the Edwardian style, rather than the blue dress shown in the film) if you wanted something prettier. For some inspiration, the Sullivan Entertainment site has a page with four pictures of Anne at different points in the films.
Bridget Jones (from Bridget Jones's Diary): Although the first Bridget Jones book came out 18(!?) years ago, she is still somewhat on people's minds because of a recent follow-up book. Consequently, now might be the perfect time to break out your bunny costume, hideous Laura Ashley dress, or ugly Christmas sweater and dress up as everyone's favorite (former) singleton for Halloween. One of the best things about Bridget is that she has a wide assortment of vices, so this could be a great excuse to smoke, drink, and/or indulge your sweet tooth (just don't make all of the questionable decisions Bridget does - it is one thing to pretend to be a character, it is another thing to emulate her in every way :). Just be certain to walk around with a diary all night (or, if you want to update it somewhat, take to Twitter the way Bridget does in Mad About the Boy) and record your stray observations, including calories consumed and cigarettes smoked. Bonus points for complaining about "smug marrieds."