Most of this information is courtesy of Zorkwiz, Dark Schneider, MaVeRiK 2002 and me!  As always - email me if you have more info...
 
Level 1:
 

Teleporter Location	Destination
2, 9	Random
13, 33	Random
18, 40	Random
19, 27	Random
23, 12	11, 35, 5 - Old Library
25, 38	25, 35, 1
32, 45	Random
39, 11	36, 21, 2

 
Level 2:
 

Teleporter Location	Destination
4, 12	14, 21, 10
3, 12	4, 3, 9 - Morgoth's Lair
10, 4	26, 35 - "Slimy Room"
12, 37	Random
24, 34	Random
33, 28	Random
36, 12	Random
38, 41	Random
40, 31	around 42, 42, 4 (Water)

 
 Level 3:
 

Teleporter Location	Destination
5, 12	17, 13, 4 - "Spinnerville"
38, 31	Random
7, 41	25, 6, 3 - Next to altar in entry room
42, 14	Random
4, 20	Random
38, 9	18, 19, 1 - Fountain & Mana orb room

 
Level 4:
 

Teleporter Location	Destination
39, 7	Random
21, 37	Random
27, 23	Random
5, 2	Random
5, 1	44, 27, 2 - Outside Aboleth Room
12, 32	Random
2, 15	Random
1, 14	Random

 
Level 5:
 

Teleporter Location	Destination
10, 45	Random
19, 8	Random
44, 45	Random
40, 1	Random
2, 16	Random
2, 13	Random
34, 22	Random