I have to agree with OC that in general it's more rewarding to create your own sounds, but there's nothing wrong with using presets, they're simply instruments, you don't see people complaining saying "piano? this is SO trite! ugh", so I don't totally understand where the complaints of lack of originality come from.
from what I can gather of the original post, the topic creator isn't experienced in sound design and is probably more looking for samples or presets, in which case absynth would be a good place to start as its presets tend to be geared towards those kinds of esoteric sounds. but if he is interested in learning to synthesize his own sounds, there are probably better options. personally for a commercial synth I'd recommend zebra, from everything I've tried it seems to have the best ease of use to options ratio and it's cheaper than absynth or omnisphere too.
for free stuff I'll second the recommendation for STS-33, it's great and I've used it in like half of my songs since I downloaded it(although I'm still using STS-11...). even if you're not a sound designer, as OC said, it has lazy buttons that can randomly generate some good sounds for you. texture http://www.kvraudio.com/get/1002.html is another good freebie that can do some unusual sounds. I find I get a lot of good strange results from FM and RM synthesis but I'm not sure what really exists as far as that goes for free plugins, I use Sytrus a lot which I DO NOT recommend as it's interface is something of an abortion, I'm just too cheap to buy new stuff :/ plus I like using internal FL stuff where possible because of the per note controls that you don't get with anything MIDI(VST) related, it's only really surpassed by samples in trackers in that regard
and yeah, just being creative, use effects in unusual ways or mangle up samples or even use totally unconventional sound sources. http://www.kvraudio.com/get/2189.html is pretty good for turning like anything into creepyness.