About a month back I checked out the 80's cult classic The Deadly Spawn which is about a meteor that falls to earth and unleashes these sharped-tooth tadpole aliens and their mother to feast on a neighborhood. It was pretty entertaining for a budget of only $25,000. It's one of those 80's flicks that pays homage to the alien invasion movies of the 50's and this one has its share of gore.
After seeing this one, I found out there was an unofficial sequel produced in Europe called Metamorphosis: The Alien Factor. Originally planned as a direct sequel, there were some issues with copyrights so they had to change the plot around. This movie concerns a government lab that conducts all sorts of genetic experiments. Scientists are given alien DNA to work with and it mutates ordinary animals. When a doctor is bitten by a frog mutant, he slowly transforms into a huge creature that resembles the mother alien of Deadly Spawn that terrorizes the facility chewing people up. This one's packed with gore and very cool animatronic and stop-motion creature effects.