Over time I've found the most effective motivation to be the deadline. If you know the next section is going live on Friday, whether it's nicely polished or just a pile of half-finished notes, you feel compelled to actually write something. My logic is that you can always go back later to change something if it doesn't work, granted that doesn't apply to a consistently rolling webcomic.
You know what you need to combat writers block? A manatee tank with floating balls with random words printed on them. The manatee will select several balls at random, and you then write your story around them.
But...i don't want to choose between fun and responsibility. Isn't there a third option where we travel to the desert to consume conspicuous cacti and just allow whatever dribbles out our brains to be absorbed by those that require our absorption?
How can you have writers block when EverQuest Next was canceled just over a week ago?! That alone is enough material to push 2 months worth of comic gold. Touch in a bit about how Daybreak split their game H1Z1 (each now dubbed "H.5Z.5") for giggles.
Oh, and there's the whole Gawker with Hogan's sex tape. What, too easy to make tabloid jokes?
The Cuban trade agreement Obama is so sought after could have a Duke Nukum joke about finally releasing his cigar supply.
Third option: create a webcomic about writer's block to delay a deadline :^)
Deadlines are hell of a motivator though. I remember banging out 7500~ or so words on a project last summer because the project review was two days later and I wasn't even 1/3 of the way through at the end of two months.
It ended up being a major success, but ever since then I only ever write seriously when I can no longer escape the deadline
What if my muse IS that shambling abomination from the multi-planar spaces between angles? Lovecraftian horrors make excellent guides, what's that Yog-Sothoth? Enact an ancient rite that will open the gateway to higher and lower planes? Well... If you think it will help me write my next book!