Sky Girls

Sky Girls and Strike Witches shares the same genre with a fairly similar setting. 

loli on mecha. you dont really have to say more.  

Both shows involve a predominantly female cast combating alien lifeforms. The use of technology is an integral component in both series. 

Although one is land based fighting, and the other is air based, they are both about girls that are experts in handling their heavy artillery that most would think only guys would be interested in. Also, even though both have competitions to show off their skills, Sky Girls is much more than that - these girls are actually involved in a war. GuP is much lighter than Sky Girls. If you loved GuP, you will adore Sky Girls. If you liked Sky Girls, you'll love GuP. I do think that Sky Girls is better, however they are both good anime series ;D 

Girls using technology to fly and fight off a invasion. The girls are also very close to each other or become close over the course of the series. And in both the main character needs to transfer because of the airforce. 

Both have 3 girls who pilot mecha over seaside towns. Otoha and Madoka are both cheerful. Ichijo and Lan are serious, and Karen and Muginami are both kinda ditzy. 

Similar theme, style, and involves plenty of action packed battles. Mecha plays a theme in both series although Sky Girls have an added flavor of romance.  

Both shows deal with teenage girls in a somewhat Si-fi situation where they learn to work with, and actually work with advanced technology to accomplish something. In the case of sky girls they are working with humanoid flight / assist suits for the post war military as test pilots. 

aliens attack earth check cute girls piloting old school planes check cute girls working under military/government orders check what else do i need to say  

Sky girls always reminded me of Eva from the start. From the suits(especially the things on their head) to the story. Except sky girls is more loli and more upbeat. 

Both feature young girls in a military-scene who fly through the air with heavy machinery doing their jobs. Also, both both started out as OAVs and have (or going to) anime series. 

Same sort of idea of saving the world...very similar. i really enjoyed both of these so.... 

Even though Jinki: Extend is more serious, both of these series are about girls piloting mecha. If you've watch Jinki: Extend then watch Sky Girls to make you feel better. 

Both are Mecha Musume shows, and even the main girl looks similar!