@Mushroom Buttons: Hiiiigh ptich (like C-9) triangle and sine waves (emulate harmonics with, well, harmonics, so if you use c-9 add f-9 or g-9 or even f-10

@ambinate: I forgot: delay can work wonders as well. So, in this example, he very first pad is just breathing, the second is triangle waves with reverb and etc, and the third is a choir, all as outlined below.
Examples galore~
Soundcloud
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@ambinate: Basic pads... are all about them suspended chords, mate. Really, though, start with layered triangle or saw waves (pitch-filtered* white noise especially works wonders), with soft attack and soft release. Use multiple reverbs on multiple sends/busses and filter them each so they have their own bands. Modulation such as phaser of chorus can help, but drenching 'em on (generally) won't make pads softer. Oh, and remember, less is more; the less you process, the more solid it would feel. Alternatively, choir synths. Filtering the lows out can help, especially if you use multiple pads in unison at different octaves.
Some people like a light distortion applied for a layer of haze.
Personally, I like vocal samples (like choirs, light breathing or held notes of acapellas) that've been reverb'd to the core and back. And then resampled at reverb'd some more.
*Like, look up the pitch of A (440 Hz or whatever) and narrowly bandpass white noise at that frequency. Then render and resample, and you have pitched noise. Can help for that hazy feeling.