Shibuya -- You might try Hobgoblin Shibuya, on Dogenzaka slope, at 1-3-11 Dogenzaka (tel. 03/6415-4243), open Monday to Friday from 5pm and weekends from noon.
Roppongi -- Directions are from Roppongi Crossing, Roppongi's main intersection of Roppongi Dori and Gaien-Higashi Dori.
Try Hobgoblin Roppongi, on Gaien-Higashi Dori in the direction of Tokyo Tower at 3-16-33 Roppongi (tel. 03/3568-1280), open daily from Monday to Friday from 5pm and weekends from noon.
By yourself but still want to hit the town? Or maybe with friends but don’t know where to go? Join the Tokyo Pub Crawl (www.tokyopubcrawl.com; tel. 070/1326-1423), which is like a party every Friday and Saturday night when up to 100 people visit three bars and a club in Roppongi. The cost is ¥2,900 for men and ¥2,000 for women (which includes a shot at each venue); the website has discounts, signup, and details. Interestingly, some 30% attendees are Japanese (many of whom come weekly), making for a diverse international crowd. Lots of fun.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.