If you just want to save for retirement, start with a financial planning book, like this one:
and here's my editorial on the investing part:
If you're thinking of spending time stock-picking or trading for fun, then there are lots of options.
Morningstar Premium (http://morningstar.com) has very good information. They analyze almost all large-cap stocks and some small caps too, plus mutual funds and ETFs, and have some good general information articles. It doesn't have the sales-pitch hot-blooded tone of most other sites. Morningstar analyzes companies from a value investing point of view which is probably what you want unless you're day trading. Also they analyze funds, which are probably the most practical investment.
If you want to be competent (in the sense that a professional investor trying to beat the market or control risk vs. the market would be) then I thought the CFA curriculum was pretty good:
However, this will quickly teach you how much is involved in being competent. The level 1 curriculum when I did it was 6 or 7 thick textbooks, equivalent to probably a college semester courseload. I didn't do level 2 or 3. I don't think level 1 was enough to become competent, it's just enough to learn what you don't know. The actual CFA charter requires all three levels and years of work experience.
If you more want to dabble, then Benjamin Graham's The Intelligent Investor certainly isn't a bad place to start, but you'd also want to read some efficient markets stuff (Random Walk Down Wall Street, or something by Bogle, or The Intelligent Asset Allocator http://www.amazon.com/Intelligent-Asset-Allocator-Portfolio-Maximize/dp/0071362363, are some options). It wouldn't be bad to just read a textbook like http://www.amazon.com/Investments-Irwin-Finance-Zvi-Bodie/dp/0256146381 which would be the much-abridged version of the CFA level 1 stuff.
If you're into day trading / charting, then I don't know much about that at all, some of the other answers may have some ideas. I've never been able to find info on this that didn't seem like it had a sketchy sales pitch kind of vibe. Honestly in a world of high-frequency trading computers I'm skeptical this is something to get into. Unless you want to program HFT computers: http://howtohft.wordpress.com/