You are probably already pretty conversant with the normal heraldic expressions and how they are used. The problem is that the bits you want to find out more about are all hidden away in little corners; this is always the case, I suppose, but most of the books will give you the general picture, without the sort of detail which you get on the HSS website's Forum. The detail on the Forum comes because the participants are really keen and so go out of their way to learn the odd, arcane and peculiar things. It is this extra knowledge which makes the Forum such a stimulating place, although sometimes I dread to open some of the threads! 

HERALDRY ON THE WEB 

On the web, there are a number of heraldic sites, but the best for a general overview is http://www.heraldica.org, although it is slightly biased against Scottish practice on the question of noblesse/gentility, which Scots regard as being the same, while the English say that nobility is as it were a grade above gentry. Francois Velde is an American enthusiast and also has a lot on chivalric orders, the sort of thing that we are not allowed to talk about!  There is also the Google rec.heraldry forum,                                                                http://groups.google.com/group/rec.heraldry  but since the advent of our Forum, this has become markedly less interesting. Despite that there is a wealth of material in the archive, from the last 10/12 years. Of course there is also the website of Anthony Maxwell, http://www.scotsheraldry.com, which includes a forum and other material, some of which he used on the Society’s website when he was webmaster. A specifically Scottish site is the Baronage http://www.baronage.co.uk which was developed by Frederick Hogarth, with its associated magazine The Feudal Herald. 

In fact the archive of the HSS Forum is as good a place as any to look, if you want to research a particular topic. Both this archive and that of rec.heraldry can be searched on any word or combination of words; you probably know to put inverted commas around a phrase which you want to search for in its exact form; without the inverted commas, the search is for any and all of the component parts.

BOOKS ON SCOTTISH HERALDRY 

As for books, if your interest is particularly Scottish, start with Mark Dennis' Scottish Heraldry (HSS), also The Lion Rejoicing by Mark Dennis and Charles Burnett (HMSO). Both are recent and well-written and available on this site.  For a fun and older book, currently out of print, try Moncreiffe and Pottinger's Simple Heraldry. For a view on the origins of Scots heraldry try Beryl Platt's somewhat contentious Scottish Hazard (Proctor Press available from Heraldry Today).   

Textbooks for any serious student of Scottish heraldry are:  

Scotland’s Historic Heraldry by Bruce McAndrew (2006 Boydell), comprehensive and detailed by our foremost Scottish historic heraldist

Aspilogia Scoticana or “Scottish Armorials from earliest times to the start of the eighteenth century” to give the full title, by Alex Maxwell Findlater (2006, HSS)

Sir Thomas Innes of Learney's Scots Heraldry (1934, revised 1956 and revised by his son Sir Malcolm 1978).  Sir Tam was an innovative Lord Lyon and the progression of his thoughts between the first and second editions is fascinating.  His closely argued theories and changes are due for re-evaluation.

Sir Francis James Grant's Manual of Heraldry (1914, revised 1924 with many later editions).

J H Stevenson's Heraldry in Scotland (1914), probably still the most authoritative, but sometimes difficult to read

Heraldry in relation to Scottish History and Art which is the text of the Rhind Lectures given by Lord Lyon Sir James Balfour Paul in 1898

The Treatise on Heraldry: British and Foreign by Woodward and Burnett (1892), which has some good Scottish stuff from George Burnett (1822-1890), who was Lord Lyon from 1866 until 1890.  Scottish heraldry along with English went into a grand slump in the eighteenth century and only recovered after the Lyon Office was reorganised in 1867 after the appointment of Burnett as Lord Lyon in 1866. Before that Lyons had appointed Deputes and there was a lack of seriousness; moreover the Depute did not have the authority required for the job.

Seton's Scottish Heraldry (1863)

Nisbet's System of Heraldry (1722) which is the bible and

The Science of Herauldry (1680) also known as Scotland’s Herauldrie (sic) by Sir George Mackenzie of Rosehaugh, the wicked Lord Advocate, which has lots of Latin and $$$$$$ attached as well. This is the only text on heraldry which has legal authority in Scotland. 

In 2002 the first purely Scottish roll of arms was published, The Balliol Roll (ca 1332) edited by Bruce A McAndrew.  It was published by the Committee on Heraldry of the New England Historic Genealogical Society and should still be available from them; their website is at http://www.newenglandancestors.org.  The HSS has started the publication of a series of facsimiles, or quasi-facsimiles, of generally 16^th century rolls of arms.  The first two of these were published in 2006 by the Society:

The Dublin Armorial of Scottish Nobility (ca 1592) edited by Leslie Hodgson

The Dunvegan Armorial (1582) edited by John and Eilean Malden 

Future armorials in this series are planned, with Lord Crawford’s Armorial (ca 1602) (sometimes erroneously called Lindsay Secundus) and the Hague Roll (ca 1592) as present work-in-progress. 

Also printed in 2006 by private subscription was the Slains Armorial (ca 1567) edited by Anthony Maxwell.  Second-hand copies of this may gradually come available.  Another book, or perhaps booklet might be a fairer description, published in 2006 was Scots Heraldry Visited by John Hamilton Gaylor.  This can be obtained from the author on gaylor@uwclub.net or by sending him a private message through the forum. 

BOOKS ON ENGLISH HERALDRY 

The standard English works are those of Fox-Davies and Boutell. Both are revised and annotated by John Brooke-Little.  His edition of Boutell’s Heraldry is probably still the best general book on heraldry.  There are many facsimile editions of the Fox-Davies Complete Guide to Heraldry, which makes it easy to find, but he is opinionated and very English and full of rules rather than the historical and scholarly appreciation of the subject Here Brooke-Little has not changed the text, but rather indicated up-dated views etc in foot-notes. General books on Heraldry, all from an English view-point, include: 

An Heraldic Alphabet by John Brooke-Little

The Oxford Guide to Heraldry by Robinson and Woodcock

Heraldry for the Local Historian and Genealogist by Stephen Friar

Stephen Slater's finely written and very colourful The Complete Book of Heraldry

A New Dictionary of Heraldry by Stephen Friar

also anything by Ottfried Neubecker and Carl von Volborth.  

RECENT WORK: JOURNALS 

For up to date matter, the best source is journals, particularly the Double Tressure and the Coat of Arms. You are presumably already enjoying the current DT, but a lot of back numbers are available and indeed the early ones have some of the best articles. The CoA is published by the Heraldry Society (England), see their website. 

SECOND-HAND BOOKS 

For used books, search on abebooks http://dogbert.abebooks.com/servlet/SearchEntry or on http://www.used.addall.com, which is a compilation of various web-lists of books. There is also http://ukbookworld.com/cgi-bin/search.pl, which has only UK booksellers. But if you want a book badly enough, it only costs the extra postage! For books which are still in print, I presume that Barnes & Noble or Amazon are the best; however with heraldry, there are never very many books in print. 

Good luck