first up guys, whoa -thanks for bringing such diverse and valid viewpoints to this post,, I'm gonna have to get back to many points like that of Kant's. Points like that of being a spiritual atheist and its connotations as girrygrrl see's it etc are enlightening.
I myself would, if not for experiences I'm not going into, probably be agnostic, but primarily humanist. Un/fortunately I can't take this stance as personal experience points (just) me towards belief and a relationship (for better OR worse) with ""God"", and even though this could be critiqued as delusional I believe many would see my logic,,even if my conclusions may include 'it' to be a bit of an asshole, and perhaps not all powerfull or even having any human characteristics, maybe just a system (so sue me ""God""). Anyway - thats for another day.
I thought a first point to bring up is in response to Sirmoonie's great response " if true (to there being a God but no afterlife). You could just thumb your nose at Him, like get completely ripped on Sunday mornings, and what the hell is He going to do you? He has no everlasting hell burning to use as extortion, and no heavenly salvation as a bribe. It would really equalize things with Him "
I laughed and completely agree to a point,, I mean "God" aint stopping me getting trashed whether Sunday or not, I'm not sure "God" would even give a shit about this next to,, say, treating others kindly,, equally ""God"" might not give a shit about whether you believe in it or not - I myself think this 'belief in God' point is only of major importance to humans involved in their tribalistic Religions, not "God",, though this is just my humble opinion, I,, unlike many, am intent on not putting words in "Gods" mouth.
But - what if you found out you yourself,, yup - you reading this now, was actually "God"? You loved every one of us and knew every one of our thoughts and deeds, but even as "God" you didn't think,, or worse knew there to be no afterlife? Perhaps this would riddle God with grief and sadness, perhaps this all knowing 'thing' would hope for a higher "God" to grant humans the wishes 'it' could not? Perhaps though this very fact would enrage certain people within Organised religion, we could and should (if this theoretically were the case) feel sympathy for "God", who loved us all just the same?
Back to my thoughts on Sirmoonie's point - like I said I'll get trashed and do as I please with my body when I want, screw religious fearmongering and dogma's. But (if your still understanding this viewpoint!?) ,, would knowing such a fact, as a human,, make you less inclined towards doing good to others? I'm sure some would see it as a greenlight to become selfish assholes,, since there would be no 'Ultimate judgement", only the laws set-up by humans,, but maybe others would still see doing as to others as one would like to be treated as being just as crucial, if not even moreso?
As mentioned by another I'm thankfully not alone in seeing this theoretical viewpoint as a hot topic (many thanks) - if only for the moral questions it generates.
And of course the spiritual ones still. For instance if you now knew there to be such a being that loved you but couldn't guarantee an afterlife, your relationship to "it" may well change,, but ultimatelly you would still be you, able to do to yourself and others what you wanted, with "God" as your witness. Perhaps some would see themselves understandably as 'gods' themselves, but the fundamental point of good and evil as I see it would still remain..
Like I've said I for one have a relationship with/ 'faith' (an ambiguous term?) in God, if not an afterlife - how the hell would I know! Death is a privelidged mystery to me. However I am very interested and a general defender of the Anton Lavey school of (completely misunderstood generally) "Satanism", - yet I still find some of their arguments (as well as philosophers) about good and bad being mere constructs dependent on what side of the coin your perceiving things as being very suspect.
Again thanks for the inspiring replies guys - I have much to learn and comtemplate thanks to you.

Hope this thread keeps running, and all POV's contemplated.
P.S (edit) - Girrlygrrl, I find your reply to be absolutely superb - and as a belief system one I hope to / wish I could embrace - it's just that at the start of your post you say " My beliefs are - there is no afterlife" ,, but after this you clearly,, to me alone - define what I consider to be an afterlife. So while I hope for our sakes in your belief turning out to be correct, I must stress that my idea of 'no afterlife' seems to conflict.. My idea of no afterlife,, (and contradictorily this may be seen as an 'afterlife' in itself!) would be death being the End, a fade to nothing, completely zero EXCEPT for ones body feeding worms, vultures (etc - personally I'd like to be fed to pigs then composted on a vegetable patch) or else incinerated (again here I'd wish that my lifeless corpse be used as heating / fuel)...
Needless to say I hope you understand by this my definition of no afterlife.. Complete non-existence...
Another very contentious subject to bring to the table (screw it!) is that I believe that though Buddhism teaches reincarnation, yet encourages all to " “Believe nothing, no matter where you read it or who has said it, not even if I have said it, unless it agrees with your own reason and your own common sense.” – a direct favourite quote from Buddha himself I believe -
anyway, though traditional Buddhism encourages a belief in the reincarnational system not too dissimilar to what you describe I think,, I believe the traditional Pali transcription of the word Nirvana, or in Pali form - निब्बान (Nibbāna) means,, and this is strictly quoting wikipedia,, "blowing out" - (to extinguish totally???).
Perhaps this gives some indication of my indifference to an afterlife perhaps being a good thing?
In a quote I'm gonna semi-jovially (dead seriously) throw into the mix just for the heck of it, a man called Kurt Cobain, originally of a band called 'Fecal matter' yet better known for his band "Nirvana",, on his last LP before suicide "In Utero" sang on "very ape" perhaps my favourite lyrics -
"Out of the ground,,, Into the sky,,, Out of the sky,, Into the ground, Out of the ground,, Into the sky,, Out of the sky - Into the dirt"
This lyric, and the Buddhist questioning I've mentioned, perfectly encapsulates (just) my interpretation of an afterlife, and I can embrace this postively.. And if I'm wrong, well, either way I think it best to try and be a decent human being towards others anyway,,and try to right my wrongs regardless - and if there was an afterlife above the one I've just hinted at, (pushing up daisies etc),, BONUS!!