There are a great many books published on Roman Coins in different languages and price points.

A good place to start is two books by Richard Plant.  These are contain many line drawings, and should help you on your way to identifying the more common Roman Coins.

Roman Base Metal Coins: A Price Guide and Roman Silver Coins - A Price Guide, both in card back at £5.95.

One of the best known authors is David Sear who has written many books on the subject. These contain great introductions, lots of additional information, many line drawings and valuations.  The most recent single volume dates back to 1988 but has recently been reprinted by Spink:
Roman Coins and Their Values, the 4th Edition ISBN: 0713478233, approx £35

This has now been replaced by a (planned) 4 volume set. The first 3 are published, the 4th due in a year or so:
Roman Coins and Their Values: I The Republic and the Twelve Caesars 280 BC - AD 96, 2000 approx £45
Roman Coins and Their Values: II The Accession of Nerva to the Overthrow of the Severan dynasty in 235, 2002 approx £65
Roman Coins and Their Values: III The accession of Maximinus I in AD 235 down to the assassination of Carinus and the accession of Diocletian, 2005 approx £55

Another book to consider is a large glossy colour single volume by Rasiel Suarez called
Encyclopedia of Roman Imperial Coins (ERIC), ISBN: 0976466406 2005 approx $75

Roman Imperial Coinage RIC published by Spink is the definitive reference of its age. Volume 4 has 3 parts bound into 1, and Volume 5 is split into 2 parts, making 11 Volumes in total. In 10 parts, it took 71 years to complete from 1923 to 1994.

1 Augustus to Vitellius Sutherland 1984  £75 / $125
2 Vespasian to Hadrian Mattingly & Sydenham 1926 £95 / $175
3 Antonius Pius to Commodus Mattingly & Sydenham 1930 £95 / $175
4 Part 1 - Pertinax to Geta Mattingly & Sydenham Sutherland  1936 £95 / $175
4 Part 2 - Macrinus to Pupienus Mattingly & Sydenham Sutherland  1938  
4 Part  3 - Gordian III to Uranius Antoninus  Mattingly & Sydenham Sutherland  1947  
5 Part 1 Valerian to Florian Mattingly & Sydenham 1927 £70 / $120
5 Part 2  Probus to Amandus Mattingly & Sydenham 1933 £80 / $130
6 Diocletiani to Maximus Sutherland & Carson 1967 £50 / $95
7 Constantine to Licinius Sutherland & Carson 1966 £50 / $95
8 The Family of Constantine Kent 1981 £125 / $200
9 Valentinian I to Theodosius I Mattingly & Sydenham 1951 £125 / $200
10 The Divided Empire Kent 1994  £125 / $200