I've only bought some cheap puzzle/strategy games like: Monstro Battle Tactics, Tales of Maj'Eyal, The Room Two. And additionally Wuppo as it is almost top rated by Steam users. You can filter out discounts by many filter on my website steamhits com

I've prepared a page: steamhits.com where one can find current discounts on Steam games. Many filters are available, so I think it can be helpfull.

For such a big sales I always use:

steamhits(dot)com/Discount/Best

for checking best discounts.

So far I bought Psychonauts for 0.99

Pirates and complete version of Civ 3 for 1$, this means instabuy!

For anyone who is not convinced - bundle's games rates::

steamhits(dot)com/Bundle/AllActive