Though I love my Beatles and my Stones, I have a guilty little pleasure for Top 40 tunes. The songstresses of the day, with their (sometimes literally) out-of-this-world fashions, make amusing subjects for a Halloween costume. Here are some of my favorite ladies who would be wonderful to dress up as:
Lady GagaA popular costume last year, but still as fun as ever in 2010. Lady Gaga is a fun, fashion-forward person to dress as if you still want to look daring, a bit naughty, as well as pop culturally current. With Gaga selling official costumes through her website, her look becomes even more attainable, but I personally prefer to see people get creative with their own interpretations.

Ke$ha For the obnoxious beer-drinking gal at heart. I toyed around with going as Miss Dollar Sign to one of my Halloween parties I'm attending, because it seems so low maintenance but like SUCH fun. Find feathers to wrap in your hair (the more twisted, wavy, and out-of-control, the better) and tons of sparkly chains to wrap around your neck and wrists. When that's done, paint heavy eye makeup on and douse yourself in glitter. Repeat. Repeat again until you literally see glitter in your eyes. If you can find a headdress or studded boots to wear, then you're golden.

Other ideas to dress as a Pop Star Princess:

• Britney Spears, in any of her mutations: innocent schoolgirl, interstellar heartbreaker in a red catsuit, Toxic mama, Madonna kisser, bald Brit with an umbrella, or the resurrected queen of the Circus that she is today, there are endless versions of Britneys to be. I recommend gathering a group of your best girlfriends and each choosing a persona from Brit's history.  
• Amy Winehouse: I was Amy my junior year in high school. I found a see-through body shirt that had tattooed sleeves, then I wore a low-cut top and miniskirt, candy pink heels, and styled my long black wig into a beehive even Ronnie Spector would envy. Then I did the requisite Winehouse winged eyeliner. It was a hit. 
• Katy Perry: whipped cream bra and cherry chapstick are not included.
• Rihanna: with her wild hair and even wilder fashions, dressing up like the protegee of Jay-Z will surely get you noticed on October 31st.  
• Janelle Monae: if you can figure out how to do your hair like a rockabilly and can pull off a tuxedo and wingtips as well as Janelle, then I encourage you to dress up as music's new darling.