Off hand, I can think of a few you might be interested in...
Fiend Without a Face - great flick with some tense, eerie scenes. Quite gory for its' time too. While you might think invisible monsters are a bit of a cop-out, once they do make an appearance they're quite cool-looking and unique. This one's a Criterion release, so the extras are top-knotch. It has a commentary, a featurette and some trailers.
Angry Red Planet - fun flick with some cool effects and monsters. There's a trailer on that one.
Invaders from Mars -Great film, very similar to 'Invasion of the Body Snatchers'. It has a wondefully eerie soundtrack and dreamlike visuals. The dvd has two versions of the film - the US cut, and the British version with an alternate ending.
Target Earth - you might not consider this a good flick, but I quite like it. A woman wakes up to find everyone else in her city has been killed by invading Venusian robots. Fun little flick. The dvd has a commentary by the film's producer, and a trailer.
Quatermass 2 - Very cool flick with some nifty Hedorah-like monsters. If ya liked 'Quatermass and the Pit' you should check out that one.
Earth vs. the Flying Saucers - you've probably already seen this one. It's a Harryhausen flick, so it's a must-have.
First Men in the Moon - another Harryhausen film, and a good one.
The Time Machine - Another favourite of mine. You might've seen this one too. It's way better than the remake, IMO. The dvd has a trailer and two featurettes.
Hope those will be of some us to ya.