References provided by A.D.King

He mentions other versions of ADE series, one related to del Pezzo surfaces (1.), and one introduced by Deligne-Vogel. He added: I think that the del Pezzo series may be closer to what you have in mind than the Deligne-Vogel one and that Philip Boalch's paper might be particularly interesting.

1. A2xA1 A4 D5 E6 E7 E8 ...

arising as symmetries of del Pezzo surfaces (or at least their intersection lattices), which probably goes back to Coble and which also seems to appear in supergravity (cf. Vafa's `mysterious duality').

Here are some references:

2. A1 A2 G2 D4 F4 E6 E7 E8

This sequence seems to go back to Deligne and is strictly finite because they are all subgroups of E8.