There is a Mitsubishi td04 in the USDM WRX, however it will not bolt up into an eclipse, nor will an eclipse turbo bolt into an impreza. The flanges are all wrong.

There are however a few hybrids that utilize the garret wheels, which you should be familiar with. However, they are still in their infancy and not in full force as of yet.

Many people just opt for the IHI VF series of turbos. They are relatively low cost and there is a wide range of options to choose from. The most common would be the VF30/34. The difference between those is that the 34 is ballbearing. There are also a few other notable manufacturers as well... Like PE, APS, and AVO. All have some pretty monster turbos that exceed the IHI turbo's in terms of price and performance. Most if not all of the later mentioned turbos are ballbearing type turbo's.

As far as your mention of combatting lag... There isn't really much that can compare to the stocker. It's so darn small to begin with. But one worth mentioning is from iON Performance. It spools quicker then stock, can hold more boost then stock, and is relatively a good value. And you can pay for more options as well, like clipped wheels, uprated WG actuators, and ball bearing cartridges. jack@ionperformance.com can answer your questions on that turbo and all it's options.

Good luck!