Hi there! I don't know how much time you have available for your trip, but this would be a good option for the order: Santiago de Chile, bus to Mendoza (6 to 8hs, several companies), bus to Bariloche (night bus, Andesmar)... From Bariloche you can visit the Chilean Lake district which is awesome as well, recommended if you have time... Once in Bariloche, you have diferent options...
1) Excursion along Route 40 to El Chalten, it is the cheapest way of doing it... It includes an overnight in Perito Moreno (not the Glacier, the town, close to the UNESCO Human Heritage Painted Caves). Then, you can stay in Chalten for ate least 2 nights if you wanna enjoy the treks available (no need to hire guide for the standard ones, the paths are easy to follow). From Chalten, 5-hour bus to El Calafate... You can spend 3 nights in Calafate and leave to Torres del Paine in Chile, there an excursion that leaves Calafate at 5am and reaches Lago Grey in Torres del Paine after a sightseen excursion in the Park, it is the best way to get there if you want to avoid taking a bus to Puerto Natales and a compulsory overnight there before taking another bus to Paine. Paine is great for trekking, let me know what type of experience you want and I can give you info about the options... From Paine bus to Natales (not much to do / see there, so go directly to Punta Arenas) and Punta Arenas. There are daily buses (except on Sundays) to Ushuaia, it takes more than 15 hours and the buses are not really comfortable, but it is the only option and the ride is nice. Now, from Ushuaia, take a plane either to Puerto Madryn (Peninsula Valdes, whales are there from May to December, in february you will be able to see penguins, orcas, sea lions and birds) or to Buenos Aires... Believe me that it does not worth busing from Ushuaia to madryn or Buenos Aires, if you compare $$$ and time spent you will realize of that, unless you are planning to visit something on the way north...
2) Bus from Bariloche to Puerto Madryn (10 hours, Andesmar)... and then, the same route but the other way round...
To visit Uyuni I higly recommend taking the 4WD excursion leaving from San Pedro de Atacama in Chile... it is about 100$ and includes all meals and 2 overnights in huts on the way along the desert and salt flats... Just remember that it's like an adventure, the huts are less than simple (no hot water), the weather is freezing at night and the excursion does not include english speaking guide (just the driver), you share the 4WD with other people (6 people total capacity)... Atacama worths a visit as well... How to get to Atacama? If you are in Buenos Aires, you can go to Santiago and then flight or bus to Calama, or you can go to Salta (Argentine NW) and the busing to Chile, Atacama is on the other side of the Andes... some helpful sites:
www.interpatagonia.com /
www.sanpedroatacama.com
Options are infinite,... hope this helps... :-)