The Happiest Hour is a good resource for finding cheap “Happy Hours” depending on the day of the week. Each friday, before 5PM, they send out a newsletter listing deals, reviews, and some comic relief. Some examples,

FREE DRINKS
Where: Hotel OZ, 177 Dryburgh St, North Melbourne.
Deal: Say thehappiesthour at the bar and receive a pot of heavy beer
When: ANYTIME!
Happy hour there tonight: 4Pm-6pm Fridays.
$2 pots, $3 wine or bubbly $3.50 basic Spirits

Provincial Hotel, 299 Brunswick st, Fitzroy,
$3 vodkas (thursdays)

Worth checking out if you work/live near the city.
http://www.thehappiesthour.com/

Related posts:

1. Countdown to Happy Hour
2. Cheap Eats on Slow Sundays
3. Beer to taste worse and cost more
4. Beer DeLuxe
5. Haircut and a beer