Here is one of my favorite tricks, which as a matter of fact I learned while recording some guitar solos for my band, back in the day. But nowadays I use it for synths aswell:
Create a synth line (You can use any sound you want, but best results are achived with a little late attack and longer release IMHO). Say, let it be a pentatonic scale progression from c3 to c4. Now play it backwards. Record/sample it and open in wave editor. Reverse the sample. Export it again.
That's basically all. Now it's playing in correct order again, but it have this nice, a little strange reversed articulation to it.
And now I'm usualy doing one of three following things:
A) Layer both samples, original one and 'enginered' one. This will give you strange, but little aural overal effect. Sounds really great imho.
B) Chop both samples up (original one and backwards-reversed one). Slice'n'dice'em both mixing them as you whish (few steps clean, then some reversed etc)
C) With this one we need to go back: Record original sample without any live tweaking. The reversed one on the other hand do with some live action on the knobs (usually i limit myself to some filter cutoff tweaks). After reversing that one in audio editor, chop it. Now, layer them over, with original going as intented and reversed one in random order. At this point, I'm adjusting each step of reversed one (velocity, pitch as/if needed, sometimes sampler's filters etc). Now it's some pretty crazy s**t. It'll sound random, yet wildly and really tasty.
Some other things I sometimes do with samples are basically in the same vein. I'm huge fan of chopping things up, so I use it extensivelly. I love vintage reel-to-reel tape recorders too
But okay, here we go:
Record your line, for example epiano or something. Transfer it tape recorder (basically, I think that it shouldn't be a great one - I use old polish machine called ZK-140, which is a piece of s**t, to be honest, but it fits the purpose nicely). And transfer it back to your pc/sampler. Chop it up. Play with it. Tape recorder thing will give you nice, vintage warmth and saturation. It's a good way for people who wants to create their own 'vinyl' samples and don't want to spend relative fortune making dubplates with samples
Generally I think the best way to learn new tricks and stuff to come up with sick samples is to read a lot about fifties/sixties production, recording and studio techniques. They were seriously limited by technology back then, so they needed to get creative. And some of their stuff is really wild, fresh even in our hi-tech times