Clarinet Fingering Systems
I thought that it might be fun to include some information about various historical (and current) clarinet fingering systems in my site. This could help identify a strange instrument's age or provenance, as well as giving you an idea of what is available out there! This won't be an exhaustive academic overview, never fear, just some examples pulled from my current collection.
Simple System 
Any of a variety of early clarinets, some having just a couple keys (late 18th to early 19th century) to a mid 19th century 13 key example like this Bb clarinet from France. These tend to have a very pure sound and play well in 4 or 5 keys (e.g. C, G, F, D and maybe Bb) and go downhill from there. Consequently, they were generally available in A, Bb, C, and Eb - although I've seen them in D and Ab as well! Great for early classical.
Simple Albert System
This is a nice example of a late 19th century Bb Albert clarinet by Rigamonti of Italy. Similar to the previous model, but having a much improved design in the right hand. Still used by Klezmer and Greek folk players. Commonly found in A, Bb, C and Eb. A little more flexible than a simple system instrument!
Standard Albert System 
This is a nice example of an early 20th century B Albert clarinet by Kohlert of Czecheslovakia. Similar to the previous model, but having in addition the front F, Eb trill, and rollers for the pinky keys. Eagerly sought by New Orleans jazz buffs as well as the Klezmer and Greek players mentioned above. Commonly found in A, Bb, C and Eb. A little more flexible than a simple Albert instrument!
Full Albert System
Like the regular Albert but with all the Bells and whistles! From the top of the instrument: 4 trills, 3 rings.
Lower stack: articulated C# vented through the tenon, B ring, LH pinky G#. These were used by some of the best early Jazz artists and some symphonic players - just about as flexible as a modern clarinet with that dark, big bore Albert sound.
Standard Boehm System 
This is what most of us think of when we think 'clarinet'. This c.1950 Penzel Mueller has the Boehm keywork that originated in the late 19th century and continues as the standard today. Flexible, good intonation, used for Jazz and Classical alike. Still available in A, Bb, C, and Eb!
Advanced Boehm System 
This Boehm clarinet by Selmer of Paris has an Eb ring and an articulated C#, additions that faciliate certain passages, trills and sharp keys. Mostly used by symphonic players, but occasionally by Jazz musicians as well. Commonly seen in A and Bb.
The end result of this line of reasoning is the....
Full Boehm System 
This Leblanc has (in addition to standard Boehm fingering): articulated C#, Eb ring on the upper stack, LH Ab/Eb, and a low Eb like a bass clarinet! The low Eb allows an alternate Bb (insted of throat Bb) and covers the range of the A clarinet as well, allowing you to transpose music and not have to buy another $4k clarinet. The extra inch of bore scale to accomodate the low Eb also gives this instrument a larger, darker sound, much like an A clarinet. Sharp keys are a breeze to play, and you'll be able to kick sand in the faces of the 'keyless wonders' around you...