I'll copy my hcl summoner build, it's quite simple:
Budget, no price limit, ladder, non ladder?
A decent pvm budget build with expensive options:
Max raise skeleton
Max skeleton mastery
Some points in revive
Some points in clay golem
Max corpse explosion
Some points in amplify damage
Some points in decrepify
Weapon: Arm of king leoric for budget option, or beast runeword in a low req axe for level 9 fanaticism for your skeletons.
Armor: Full trang oul's set for budget choice. Enigma is the expensive best armor option.
Helmet: Harlequin crest helmet, or a good rare circlet.
Gloves: Magefist or frostburn, or good rare gloves with resists.
Shield: Homunculus or +3 skills boneflame. Spirit is a good budget option, but has high strength requirement.
Rings: Soj or bk is the optimal choice because of the +1 skills, but they are expensive. Otherwise, anything can be used for the situation. For example nature's peace for nihlathak.
Amulet: Mara's kaleidoscope, but it can be expensive. Seraph's hymn is a cheap +2 skill booster, but has no other stats for necro. Eye of etlich and highlord's wrath both has +1 skills. Otherwise, use what you need, a good rare amulet perhaps.
Boots: Marrowwalks can boost skeleton mastery by +2, but any boots that boosts whatever you are lacking is a good choice.
+1 Summon skills grand charms
Whatever you need for small charms; Life, fr/w, resists.
Can use call to arms on switch if you don't mind recasting all the time. Otherwise, keep a gull and magic find shield (milabrega's orb or rhyme runeword) to boost magic find at boss battles.
Merc; Might merc is the obvious choice.
Weapon: I have read that conviction aura from infinity is the best, because it lowers enemy defense by a huge lot, making your skeletons hit every time. But i have not tried it myself. Otherwise, pride boosts damage a lot through concentration.
Armor: Fortitude or treachery
Helmet: Life leech helmet, like andariel's visage, vampire gaze, or crown of thieves.
I personally do not use corpse explosion, but it is obviously a very powerful skill. Use amplify damage first, to boost the 50% physical damage. Use decrepify at bosses in combination with clay golem to slow them down to a near stop.