Both Borderlands titles, along with a Borderlands Season Pass, are discounted today on Xbox Live as part of Microsoft's ongoing "Countdown to 2013" holiday sale.
For today only, Borderlands 1 is available at 50 percent off, from $19.99 down to $9.99. Borderlands 2 is available for 33 percent off, from $59.99 to $39.99. Finally, the Borderlands Season Pass can today be purchased for 25 percent off, from 2400 MS Points to 1800 MS Points.
Microsoft's "Countdown to 2013" sale began Dec. 18 and runs until Dec. 31. A full list of soon-to-be discounted games, as well as titles that have already passed their one-day discount date, is available here.