If you go through Barlow's Guide to Extraterrestrials, you can find a lot of "really alien aliens", at least in appearance. As for alien psychology, as all of these were produced and written about by human writers, you are a bit out of luck. Truly "alien" psychology is likely to be totally incomprehensible by human beings.
The basic needs of a sophont are unlikely to differ terribly. Basing off of Maslow's Hierarchy of Needs...
- Air
- Water
- Food
- shelter *
- safety
- Affiliation **
- esteem **
- cognitive enrichment **
- aesthetic enrichment **
- Self-actualization ***
- Self-transcendence ***
* exactly how much and from what varies widely. Some sophonts in their native habitats might not need this - much like the !kung (kalahari bushmen) or the hawaiians pre-white contact.
** the means of showing it vary widely, as do the requisite amounts. This is where alien begins.
*** According to Maslow, most don't reach these
Given maslow's hierarchy, until we get to the need for affiliation, we really are only differing on what constitutes food, and in the case of aliens, "water" might also be ammonia or some other hydrocarbon.
Likewise, its unlikely that anything other than oxygen, chlorine or fluorine can serve as the oxidizer for life forms. And PC's aren't likely to be interacting with Chlorine or Fluorine breathers. (Their atmosphere reduces us, ours ignites them.)
And since amino acids occur in clouds in space, the odds are good the known ones are pretty likely to be the basis (tho' in subset) for most life, so food is likely to be at least recognizable as such. And while a lot of it might make one very sick due to incompatible amino acids...
So next we get to social needs. To be a culture axiomatically requires group affiliations. If they don't require affiliation they cannot be a culture. So... any sophonts we're likely to deal with are likely to have some level of need to belong to a group.
Once we have a need to be part of a group, we can start into the practical alienness: typical group size, bond strengths, multiplicity of memberships, typical bond durations... Humans tend to identify most strongly in the band of 20-30 individuals, and such groups can be lifetime long.
For aliens, we can rule out a large number of psychological traits. A successful technological alien culture can NOT be entirely loners. It must allow for transfer of information geographically and temporally. It must provide for the food, water, shelter, and affiliation needs of its members. It must not preclude population growth (when it does, the culture self-extinguishes). It must not result in too much insecurity (if it does, revolutions will happen until a relatively more secure form evolves).
Defining the outer limits really helps to create something that won't engender disbelief. If you have (as a few in Barlow's Guide do) cultures which exceed those bounds, you have a culture that is dying. Pierson's Puppeteers are about as alien as can be functional... they have the same basic needs... but their individual reactions are quite different. And quite appropriate for their postulated zoological origin species.