- Once you have played for a while you might want to look at some specific variations: for example, The Italian Game {D} (80K) for White or Black is probably all you need to know for the next year (Word 6 version with Tilburg font for download here).
N.B. Some of these booklets convert to hundreds of Kb of HTML with 8x8 GIF elements, so, I've used text-only diagrams here. If you want USCF-style diagrams instead of mine, try here, and if you have a good connection here's the Italian game {D} with GIFs (400k).
- After that you might want to look at Playing White against odd Black lines {C}, Playing Black against 1. e4 {D} [incl. Two Knights' Defence (*)] and Playing Black against 1. d4 {C}. I also have a sneaking fondness for the Petroff Defence for Beginners {C} as Black. [(*) I'm delighted to say that the Wilkes-Barre line has its own web pages at Echecs.]
If you are curious to expand your repertoire, having got the hang of attacking play and tactics, you might want to reconsider your basic Four choices in the opening {C}. Also, Steve Martinson described some openings to look at if you have had enough of 3. Bc4.
The latest addition to these opening guides is The Ideas behind the King's Gambit {B}, with an accompanying handout on the Variations of the King's Gambit {B}. [ I incline more to Lombardy's view that "at the amateur level, anything is playable" than the master view [ (1), (2) ] that all such openings suck. Well perhaps they do, at master level.]
[To see what this one looks like on paper there is 700k of PostScript on FTP]
I also posted something on Gary Lane's book (an author I usually admire, and a book which Tim Harding has praised).
There are some dedicated pages on the BDG from Jyrki Heikkinen (with superb stuff on the Diemer-Duhm Gambit, a related Anti-French line: a model of how to present chess openings on the Web), Tom Purser (editor of Blackmar-Diemer Gambit World magazine) and David Flude. There is even a BDG newsgroup in existence, but there is little or no relevant traffic on it.