Here's a list of all the artifacts that I know of that provide access to spells. Artifacts with secondary powers that I am not listing are things that provide scrying abilities or bonuses against certain types of creatures.

#	Artifact Name	Known Properties	Alignment	Owner	Secondary Power
6	Ring of Axardil	Command +10	N	N. Gondor	Access to Teleport
7	Nazguaga	Mage +30	E	-	Access to Dark Summons
15	Tinculin	Mage +40	N	-	Access to Spirit Mastery
17	Horn of Fear	Combat + 500	N	Dwarves	Access to Conjure Mounts
18	Tablets of Dark	Mage +15	E	-	Access to random lost list
19	Staff of Storms	Sailing	N	-	Access to Dark Summons
21	Staff of Earth Mastery	Mage +20	N	-	Access to Conjuring Ways
36	Suimbalmynas	Mage +20	N	-	Access to Conjuring Ways
86	Nallagurth	Combat + 750	E	Witch-King	Access to Spirit Mastery
101	E Voronwe	Combat + 500	G	-	Access to Teleport
102	Durin's Axe	Combat + 750	N	Dwarves	Access to Conjuring Ways
133	Dagger of Green	Combat + 500	N	-	Access to Conjuring Ways
135	Elenruth	Combat + 750	N	-	Access to Spirit Mastery
152	Turantir	Combat + 500	G	-	Access to Teleport
168	Ancaruin	Combat +2250	G	-	Access to Teleport
169	Gurthang	Combat +2250	E	-	Access to Spirit Mastery
170	Anguirel	Combat +2250	N	-	Access to Dark Summons
180	Fuinrako	Combat +2000	E	-	Access to Teleport
185	Headband of Sla	Mage +10	N	-	Access to Conjuring Ways
187	The Black Book	Mage +10	N	-	Access to Teleport
188	E Mere Vardo	Mage +10	G	-	Access to Spirit Mastery
189	The Blue Ring	Mage +10	E	-	Access to Spirit Mastery
190	Staff of the Wander	Mage +15	G	-	Access to Teleport