Have two designs which I would like to try designing sometime.
Thunderbird Alloy Interceptor
The Thunderbird is a new fighter design which uses Alien Alloy instead of more mundane materials for both its outer hull, allowing it to better survive glancing plasma strikes, and its internal structural supports, allowing it to reach speeds and make turns which would have literally snapped more mundane fighters into pieces. Beyond that, it also uses alien alloy in its engines, allowing them to run far hotter, and at a higher rate, then would otherwise be possible. These factors allow the craft to reach far higher speeds and maneuverability levels then any previously designed terrestrial aircraft, which should make it a far more effective craft when deployed against the alien vessels. The Thunderbird is armed with a nose mounted Railcannon and two wing mounted missile bays which are equipped to use Avalanches or, should new missiles eventually be designed, other munitions.
HWP-Railgun
This armored and automated drone can be operated either from the Skyranger or, should a connection be available, from any XCOM base. However, the operator does not have to decide every last action for the drone, as it is equipped with computer systems that can handle many minor details itself, based somewhat off the computers that allowed for the Mars Rover's remote management. Instead of the Operator driving the drone around like he or she is in a FPS, instead the Operator assigns targets and tells the drone where it needs to go, after which the computer systems can handle all the minor details like aiming the gun and choosing the exact path. Weaponwise, this HWP is armed with an upscaled railgun weapon that is supposed to be equal to a heavy machine gun (if with far more penetrative power) in use, as well as a small box launcher full of at least four mini-rockets for use against more heavily armored foes or when splash damage is needed. As well, the drone is armored in alien alloy to make it resistant to plasma.
Also for people who want a new outpost down in South America...
Well, this outpost and its ample hangers and air-focused workshop space will hopefully be useful when the UFOs next visit.
Argentina Airbase Outpost
This outpost is designed to extend XCOM's presence away from Europe and allow for faster and better equipped responses to alien attacks in the Americas. Unlike the island base it is not fully underground, instead depending upon heavy jungle cover to keep it from being visible from orbit. However many facilities are extended underground for easier defensibility and more working area. As well they are all connected underground to avoid the need to carve potentially revealing paths between the buildings. While the outpost does have a basic laboratory facility for examination of battlefield gleanings, its primary function is to serve as a amplifier to XCOM's air wing capabilities, and as such the majority of its space is dedicated towards hangers for XCOM craft, workshops to maintain and build more craft, and a few barracks so the Skyrangers will have soldiers to deliver. As well, there is also a liason's quarters with all the gear and fittings needed to support use of local InterAgency Cooperation Teams when they must be called in. If attacked, the base does have anti-air missile batteries as well as a defensive layout that will turn any attempt by the aliens to seize the base into a very nasty tunnelfight that will hopefully give the rest of XCOM time to send help, but the Outpost's primary defensive measure is supposed to be stealth.