there are 3 standalone Arpeggiators I know of:
1) Oberheim Cyclone
2) Waldorf Gecko
3) MAM MAP1
1) and 2) are no longer available new since waldorf and oberheim do no longer exist.. (well if you count viscount in as "oberheim" they do.. but it's more the paper not tom oberheims company!) .. the gecko was a very small device to be controlled by midi with one knob to set all parameters..
3) is about 90€ and is still being made by MAM germany. it'S quite like the cyclone..
the coolest Arpeggiators also have "TR-like" step programming like the Korg microkorg or complex pattern settings like the Waldorf Q had (you could set glides, random notes, step shifting etc.. and save it with the patch).
the normal "standard" arpeggiator today offers poly arp'ing with some user patterns that sometimes remind of little step sequencers, others are more basic, like one of the first Arp'ers ever (Roland Jupiter 4).
but they all have these parameters: up / down , alternating (up/down), sometimes random
and octave settings: this means: the chord will be played again but one octave higher! so a setting of 3 with one note pressed and "up" mode will play the "assimilate" them by skinny puppy ;) (hope you know it..)..
and no: there are not too many stand alone arpeggiators ...
later ones will also accept the VELOCITY that you played!! .. this makes a lot of "groove" especially if you can skip and set the "steps" like on the microkorg and the jupiter 6 "europa" expansion..
older ARPers got a trigger in jack , a trigger will play the next note, you could trigger it by some ind. out of a drum machine or like that.. so you can have more control over the rhythmic pattern.. a TR808 or electribe will do it fine..
newer ARPers will have MIDI clocked triggering.. if it is a cool thing, it can still be triggered externally by any audio signal..
there qre quite a lot of vintage synthesizers with arpeggiators aboard - some names:
Roland Jupiter 4, 6, 8
Roland 4CV keyboard 184 (belongs to system 100m)
SCI Pro One
Korg Mono/Poly, Poly61, Prophecy, Z1
Waldorf Q series, XT, Microwave II
Arpeggiator @ WIKI
etc, / to be continued..