I have a site for selling ancient coins and books about them (books below). My contact info is prominently on the pages:
http://augustuscoins.com/index.html

which has had its Byzantine page:
http://augustuscoins.com/Byzantine.html

and its Constantinian coin page:
http://augustuscoins.com/Constantinian.html

completely revised and the other pages changed, too.
The site has five long pages, so please look around. Recently I added quite a few Constantine-era coins in nice grade at prices significantly lower than elsewhere. (Confirm this for yourself.)
  
I have some important and desirable coin books (shipped to the US only), on the literature page:
http://augustuscoins.com/numislit.html
including (but there are many more--take a look)

Sear's Greek Coins and Their Values, volume II (Asia). A very good copy with no marks except the former owner's name on the flyleaf.  [$25 + $4 shipping]

Late Roman Coins In the Dumbarton Oaks Collection [Arcadius (included) to Anastasius (excluded)] by Grierson and Mays, which is a massive hardcover book of 499 pages and 37 page-plates with 955 coins well-photographed lots of excellent commentary, charts, etc.  Nice dustjacket. I love this book for very late Roman coins. It is much like the Dumbarton Oaks Byzantine catalogs, but for earlier coins. It is on Amazon, used, lowest at $90. Here, an excellent copy, only the former owner's name in pencil [which could be erased] on the flyleaf, for $75 + $8 shipping (it is heavy!).

The large two-volume book by Estiot on coins of Aurelian and Florian, "Monnaies de l'Empire Romain, D' Aureline a Florien, 270-276", with 456 pages in French (most lists, tables, and coin IDs, easy to read), plus 100 page plates and 16 pages of color enlargements and many tables. This copy is excellent.
None on Amazon. AddAll at $199 or $220 but shipped from Europe.
Here, a very good copy at $180, reduced to $165 including shipping in the US only.

Celtic coins:
Kelten im Osten, Sammlung Lanz, by Michaela Kostial. 2003. Hardcover. 8 1/2" x 11 3/4". 195 pages. 1047 coins. None on Amazon. Seems sold out everywhere. Try a search yourself. [$139, reduced to $119]  (The most important book costs less than even a single one of most of these coins!)

Read French?  A. Heiss, Description generale des Monnaies Antique de l'Espagne [Ancient Coins of Spain] 1870, Forni Reprint (The date of the reprint is not given in the book, but it looks old), in one large volume, 548 pages plus 68 plates of line drawings. 9" by 12". 2" thick. Maroon hardcover. No marks. Some foxing. Very good condition. Remarkably nice. This title sold for $300 + fees in a 2012 auction. [Mine, in nice shape, no problems, $49+$7 shipping in the US only] 

Many many other books and catalogs that I will not list here. That page is worth scrutiny. Books and catalogs help you understand what makes coins interesting and, therefore, valuable. I love coin books!