Shogouki. Could it be anything else? Granted, it doesn't have as many ways to cause large explosians as I normally like on a mech, but I still thing it's awesome.
The A. S. Arbalest from Full Metal Panic. I love it. Two chainguns in the head and a shotgun ( which fires explosive rounds) coupled with the Lamba Driver system makes for one very cool mech.
Deathscythe, from Gundam Wing. Yes, I am aware that the entire design is incredibly silly. Yes, I am aware that the scythe is an incredibly stupid weapon. But nobody can deny that it looks great.
The A.S. Venom (sometimes called the "Codarl") from Full Metal Panic. Very stylish looking mech with the hair and all, and is seen to use a wide variety of weapons (including some sort of bizzaro-gunblade style weapon). Also equipped with a Lamda Driver like the Arbalest.
And the Tachikomas from GitS, of course
Now, as for my favourite battles:
- Nigouki VS the Ryousanki in EoE. About the only mech battle I've sene which doesn't have random explosions everywhere, but that's made up for by the masses of blood
- Arbalest vs the MP Venoms in Full Metal Panic. This is probably my all-time favourite battle out of any anime ever; we get to see Sagara really cutting loose with the Arbalest. Very fun.
- Wing Zero vs Epyon in Gundam Wing. The entire damn series was building up to this fight, and it didn't dissapoint at all.
Well, that's my list.