• Irving Kaplansky's unpublished material on Lie superalgebras.
• liealgebras yahoo group (dormant, but still contains some interesting old discussions).
• Lie crossword by Rutwig Campoamor.
• Openess of exact complexes and semisimple Lie algebras by Leonid Positselskii.
• Bianchi's classification of 3-dimensional real Lie algebras by Bob Jantzen.
• Arkhipov and Positselskii on representations of affine Lie algebras.
• An identity which satisfied in all associative algebras and the Cayley-Dickson algebra, lies in the radical of a free alternative algebra.

finite-dimensional (semi)simple Lie algebras of characteristic 0

• Tony Smith's huge collections of material on classical and exceptional Lie, Jordan, Clifford, octonion, algebras and groups, symmetric spaces, etc...; particulary, on graded Lie algebras.
• E₈:
  sci.physics.research thread "Structures preserved by e_8" (gradings in simple Lie algebras, exceptional algebras, KKT construction, etc.)
  Kostant on E₈.
• The Atlas of Lie Groups and Representations: [umd.edu] [liegroups.org]
• Lattice of subalgebras of so(1,3)
• Chameleon problem and the root system of type A_2 by Ignat Soroko.
• Invariant tensors and recurrent formulas.
• The Unipotent Muffin Research Kitchen - a database.
• Пьер Менар, автор теоремы Пифагора by kapahel.

computations

GAP:

• LieAlgDB package - a database of Lie algebras of small dimension
• Small nilpotent Lie algebras by Csaba Schneider.
• a program for dimensions of representations of simple Lie algebras by Skip Garibaldi.
• GAP and LiE computations with Lie algebras by Jan Draisma.
• subalgebras of simple classical Lie algebras
• FPLSA - package for converting finitely presented Lie algebras into structure constant algebras.
• SLA - package for computations with simple classical Lie algebras, including automorphisms of finite order.
• Semidirect product of Lie algebras

other:

• Pavel Grozman's SuperLie Mathematica package.
• LiE [open source] Computations in classical Lie algebras and Lie groups. online interface.
• simplie - computations in and visualization of root systems of classical and Kac-Moody Lie algebras, Java-based.