I will be visiting Nara the day after tomorrow.
Arriving at the Kintetsu station, visiting Todaji, then some free time and leaving by JR Nara station.

Which others tempels should I visit to catch the two WHS in one day?

Hmmm editing doesn't work...

I will be visiting Nara the day after tomorrow.
Arriving at the Kintetsu station, visiting Todaji, then some free time and leaving by JR Nara station.

Which others tempels should I visit to catch the two (Nara and Horyu-ji) WHS in one day and how should I get there?

I'm very envious, however I have no experience of Japan at all so can't offer any practical advice. From my desk I saw Horyu-ji has only two components. The main cluster seems to be by far the bigger and more photogenic. The secondary one (Hokki-ji) is slightly closer to Nara, with the inscribed area of Yakushi-ji nearby, but the public transport connections didn't seem that useful.

Sorry that isn't much use but I hope it is fun.

I 'did' Nara and Horyu-Ji on the same day also, back in 2000.
I reached Horyu-ji, which is kind of a suburb of Nara, by train.
You can search http://www.hyperdia.com/ for the train schedules, the ride takes only 10 minutes and seems to be very frequent

I just came back from Japan last week and I had the chance to stay there for 2 months so I was able to visit all the WHS as well as the T-List.
For Nara, I spent a full day there and I did not even enter in all of the components (I saw only Yakushu-ji and Tôshôdai-ji from the outside because all these sites are rather expensive). If you like gardens, the Isuien Garden not far from the Todai-ji is really worth it although a bit expensive (800 Yens).

For Horyu-ji, the Hokki-ji area is much less interesting than the main cluster. It can be reached by a 15 minutes walk from Horyu-ji temples but then the bus to go back to the station are not so frequent and I had to wait almost an hour.