X-Wing : For PC/Mac
X-Wing Builder (http://xwing-builder.co.uk/build)
Star Trek : For IOS, Android and Mac
Space Dock (http://spacedockapp.org/)
As far as Android devices go: I use X-Wing Squadron Builder (https://play.google.com/store/apps/details?id=es.eko.squadronbuilder&hl=en_GB).
But I also have X-Wing Companion (https://play.google.com/store/apps/details?id=com.guidokessels.xwc&hl=en_GB) around as it's a really handy reference for various things, say you're after a specific card or somesuch - it'll let you know what sets it comes in.
I have both of the ones Pete mentioned on my phone. I think they are Android only so may not work for you Apple users out there!
For browser based builders I use this: http://xwing-builder.co.uk/build (http://xwing-builder.co.uk/build)
I've also seen a random squadron generator talked about on BOLS http://fabpsb.free.fr/gindex.php (http://fabpsb.free.fr/gindex.php). Might be fun for some themed lists/fun games