I am not currently studying Aikido (although I'm in the process of finding a dojo), I have been practicing Neijia (Chinese Internal Arts) for the past few years.
To answer AikidoNate's question in regards to the styles of Tai Ji, there are the following "main" styles: Chen, Yang, Wu and Hao (also known as Wuu) styles. There are some other styles as well such as the Sun and Orthodox Tai Ji, but what you will see the most is probably Yang style.
There are quite a few Yang style teachers around, however be careful as many of these teach Tai Ji for health only, i.e. with no martial applications. There are more and more people teaching the applications these days but they are still in the minority. BTW, when I say applications, I don't mean just doing push hands and the forms, but you should probably see "techniques" taken right out of the form in addition to San Sau which will prepare you for free fighting.
As to which style of Tai Ji would go well with Aikido, I think it's a matter of personal taste. Most likely you won't find too many instructors that teach applications to the forms in your area so you may only have one choice.
Personally I would suggest for anyone looking at adding another style to their Aikido (and would like to stay within the "internal art" framework) to look at Ba Gua as it seems to fit more in with the footwork and the spiraling patterns of Aikido. Now that I have seen and participated in classes at a few different Aikido dojo I can see more and more similarities between them. Of course I may be way off base as I haven't even scratched the surface in Aikido (or Ba Gua for that matter).
Just some thoughts from the cheap seats.