Borderlands GOTY edition is currently 75% off on steam, this purchase includes all DLC. Borderlands 2 has received a permanent $20 price reduction and is also 66% off bringing the price down to $13.59, unfortunately this sale does NOT apply to DLC.
In the UK... Borderlands GOTY - £4.99 Borderlands 2 - £10.19 USA have a better deal (£10.19 = $15.46) but you should still get it if you want it. This is for this weekend only, people, so if you are going to get it, get it now.