I'm a bit of an accessibility fanboy. I think when I start to specialise it is an area that really interests me, as it is something that we can make a BIG difference in.
I was fortunate enough to have a workshop with Derek Featherstone, and picked up an awful lot from him. I also had some really useful email guidance from Chris Mills that pointed me in the direction of further reading, and tools.
There are a lot of good books I can recommend:
... are a few that I found great reads.
The first book is a good overview and simple fixes.
The Rosenfeld book has some great tips to ensure accessibility needs can be brought into persona creation.
The last book is the most technical, but has some great examples.
I'd love to read more on WAI-ARIA, but haven't quite found the resource I'm looking for (apart from the obvious stuff - I'm more interested in practical examples).
I have had some big wins at my place of work, which I'm really happy with... for example - my arguments led us to jump on RWD only a few months after Ethan Marcotte's post (it just made sense), I pushed em's and we lost the pixels - I changed all forms (thanks to Luke W's book!).
So much that I've found with accessibility is that if you fix a problem for one person, you actually find that it has good impact on others.
An old (and now broken) example that I made for a presentation: