Since I started work a year ago, I've been reading as many software books as I could get my hands on to improve my programming chops. I've recently come across some really nice free resources that are both very useful and quite short and sweet.
Domain Driven Design Quickly is a really good summary of writing software using the Domain Driven methodology. Its only about 80 pages and really useful. It explains some useful patterns eg Repository, aggregates and others.
Foundations of Programming is more .net orientated but a really good read. It discusses some of the good frameworks out there like NHibernate and has a nice intro into unit testing. It also has a really useful chapter on memory with .net.
My next free ebook that I will read is Pablo's SOLID Software Development which to be a great intro into using the SOLID principles while developing.
While researching this post I came across this link from StackOverFlow which gives a really good list of Free ebooks. So hopefully everyones favorite language is covered.