Ways to increase Darkvision?

[muktidata]

What are some ways for a Lesser Aasmir Cleric (CL 8) to boost his 60ft. Darkvision? No templates or class levels, please.

[altpersona]

that leaves feats and spells?

[Maat Mons]

The midnight pupils trait (Dragon 356, p89) extends your darkvision by +60 feet.  The down side is “you can only see through your darkvision.”  It explicitly says you only see in black and white.  You may also be unable to see beyond the 120-foot range of your darkvision. 

The nightsighted trait extends your darkvision by +10 feet. 

A ring of spelunking (Dragon 323, p88) doubles the range of your darkvision.  It also gives you a +10 competence bonus to knowledge (dungeoneering) and lets you use reduce person on yourself 3/day.  It costs 37,000 gp.  You might be able to get a cheaper version that only has the darkvision-extending function. 

[muktidata]

that leaves feats and spells?

And items, yeah.

[Ithamar]

Ebon Eyes is a level 1 cleric spell that might be of use.  But the spell is poorly worded, in my opinion, so I'm not exactly sure how far it will let you see in the dark.

[Bananaphone]

One of these 3 feats may be useful to you.

Planar Touchstone (The Blinding Tower) increases your existing Darkvision by 30 ft.  Also grants 6 uses of a Cure Moderate Wounds.
Source: Planar Handbook

Devil's Sight increases your existing Darkvision by 60 ft.  Also allows you to gain Blindsight out to 30 ft. for 5 rounds/day per Devil-Touched feat you have.
Unfortunately it requires Devil's Favor as a Pre-requisite... and it might not be compatible with an Aasimar, heh.
Source: Fiendish Codex II

Pierce the Darkness doubles the range of your Darkvision for minutes per Character level.  Takes a Standard action and use of Turn Undead to activate.
Source: Races of Stone