I don't know of anything in particular, but check out Libris Mortis (which has feats like Fell Animate), Book of Vile Deeds, or Ghostwalk.
And if you're actually summoning undead with spells that are conjuration/necromancy (are there such?), check out the various Completes for a bunch of feats which boost summonings:
Echoing UA's Specialist variants, Focused Specialist from PHB2, and just about any summoning-centric Reserve feats
To paraphrase what I've written elswhere:
1) Check out the Feats (esp. Reserve Feats) & Alternative Class Features:
Imbued Summoning, PHB2 p92 (summoned critters arrive w/beneficial spells)
Cloudy Conjuration, CompMage p40 conjurations accompanied by a cloud of sickening smoke (CompMage p40). The cloud is similar to a Fog cloud spell, and doesn't affect creatures summoned by the spell.
Dimensional Reach reserve feat: if you have a 3rd lvl or higher conjuration spell, you get an at will mage hand effect, and you also get +1 bounus to caster level for conjuration (summoning) spells. (CompArc p41)
Summon Elemental reserve feat: lets you briefly summon elementals, and also givs a +1CL on summoning spells. (CompArc p47-8)
Focused Specialist ACF: give up 1 additional school of magic and one spell slot per level and gain an additional +2 spells in your specialty school (in addition to your initial +1 spell for specialization). That's 3 per level within your specialty.
Abrupt Jaunt Alternative Class feature (ACF): a 10' at will teleport (PHB2 p70)
Residual Magic tactical feat: lets you apply a single metamagic feat for free to a spell that follows a spell that had been cast with that metamagic feat (CompMage p46). That would let you get a metamagically enhanced summons spell for its usual cost.
Rapid Summoning ACF: Give up familiar to drop SUmmon Monster casting time from 1 full round down to 1 standard act. (UA p60)
Enhanced summoning ACF: give up Scribe Scroll and Wizard bonus feats to gain Augmented summoning and have tougher, stronger, less dispellable creatures (UA p60)
Metamagic School Focus: 3x day, reduces the cost of applying a metamagic feat to a spell by 1 level- +2levels becomes 1, 1 becomes zero, etc. (CompMage p45)
2) Summoner Domain, CompDiv p141 (adds +2Cl to summon spells). Combine this with Domain Wizard ACF, CompChamp p52, which lets a Wizard exchange a Wiz bonus feat for access to a Domain's granted power. If the PC has any Cleric levels, he gets full access to the Domain.
Combined with the reserve feats I mentioned before, you'd be adding +4CL to your summonings.