Dirty tricks.

Okay, spill. What are some of the cheapest and most "unfair" tactics you've used against the buggers?

This 'cheap trick' (but it's for the good of the planet!) has served me well, but it can be a bit maddening to put into play. It's quite simple, really: when I find the blasted alien ship (and this works best on medium scouts), I post oh, about four soldiers with high reactions. All of them face the door and are positioned so that any alien trying to get out is quite dead.

Standard Demolitions: I enjoy seeing Sectiods standing near Cyberdiscs. Less targets to shoot at.

I've also noticed that if you use a grenade on a Cyberdisc, it will NOT explode. However, if it gets shot, it WILL go up.

If the top has been blown off of the smaller UFOs (Large scouts in particular), I sometimes lob a grenade or three in there.

I carry primed alien grenades on all of my soldiers if I'm going into combat against Cryssalids, just in case.

Gee, I love terror ships... especially when I can get my rocket tank in there.

This has only happened once, but have ye ever tired of playing "Hunt the last alien" on a terror mission? Did you have laser weapons? I clear-cut the entire town.
It took forever, but I got the bastard.

Nutty things you have done?

My own list:
Taken a Cryssalid LIVE with a Stun Rifle.
(More to come)