Personally, I found Antoniou & van Harmelen's "A Semantic Web Primer" to be very useful. I felt like it covered a lot of ground at just the right level- enough to explain what was going on and why, but not so much that it got bogged down in pointless detail. However, YMMV- I know some people who didn't care for it.

It's a little bit dated at this point, but Shelley Powers' "Practical RDF" was also helpful- but, again, I got a lot more out of it once I'd read Antoniou and had internalized the whole RDF thing at a "30,000 foot" level.

BTW, I just Googled for the Antoniou book to make sure I had remembered its authors correctly, and it turns out that one of the first results is a PDF version of the entire text. I don't know what it's doing up online, but grab it while it's hot. If it's helpful, Powell's has a couple of used copies:

http://www.powells.com/biblio/1-9780262012423-2

This is a good quick overview of RDF for programmers: http://rdfabout.com/quickintro.xpd