With a fair wind, some good science, and perhaps a bit of luck here are the five that could be returning- in addition to the previously mentioned woolly mammoth.
1) Sabre-toothed tiger - there are well preserved specimens in tar pits in Los Angeles. Though to date, a sequence hasn't been isolated as the tar makes extraction difficult.
2) Giant Beaver - only died out about 10,000 years ago, so well within the range of having good portions of its DNA intact. Its habitat ranged from Alaska to Florida so there's a chance of finding well preserved specimens.

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3) Tasmanian tiger - the last Tasmanian tiger left the planet in 1936. There are very well preserved tissue samples, making it more likely for scientists to get viable DNA to produce a genome sequence.
4) Woolly rhinoceros - not really heard of as much as woolly mammoths, but many fine specimens have been found in the permafrost.
5) Giant Sloth - We've not seen its kind for around 8,000 years, but several specimens have been found with plenty of hair samples. And hair is a good source of DNA.