Sprint seems to have a good relationship with HTC, Samsung, LG, and RIM who keep Sprint supplied with a steady stream of Smartphones. Motorola is getting cozy with Sprint as well as the new partnership with Apple.
I'm sure nobody would argue with new offerings from Nokia or Sony. It seems like good money that Nokia will soon make it to Sprint with Microsoft pushing the WP platform the best they can. Sony would be a very nice addition to the lineup.
That leaves Huawei, Pantech, Sharp, Casio, Palm (if they make a resurgence) and Lenovo as the rest of the current smartphone makers who could possibly start delivering Sprint phones. Huawei seems like the most desirable out of this crop with their new line of phones raising a lot of attention. Lenovo makes a "tabphone"or "phoblet" similar to the Samsung Note. Casio is known for tough devices that are a bit lagging in modern technology. Palm has offered phones on Sprint in the past but have dropped virtually out of competition with the rest of the field.
Amazon and Facebook could enter the market, but wouldn't likely release a premium, high end type phone.
If Sanyo decides to reenter the game, they always seemed to make good phones.
What manufacturer(s) would you most like to see deal their devices on the now network?