So to get the ball rolling:
The Astros have three significant free agents hitting the market:
Starting pitcher Scott Kazmir, who started very strong but tailed off at the end of the season - season ERA of 3.10 but doesn’t go deep into games, only 183 innings in 31 starts;
Outfielder Colby Rasmus, who was a slightly-above-average offensive player (.238/.314/.475) and then went crazy in the postseason. He actually had a higher OPS (1.760) during the division/LCS than Daniel Murphy. He can play centerfield competently, though he’ll be mostly a left fielder if he comes back to Houston.
Lefty reliever Tony Sipp, who had a sub-2 ERA and >10 K/9. He’s 32 and it was the best season of his career, though his previous season (also with Houston) was pretty good too. The strikeout rate has been consistent across his career, but he greatly improved his walk rate in Houston.
The team’s biggest weakness was lack of offense from 1B/DH - Evan Gattis had a .285 OBP, Chris Carter couldn’t hit .200, and others tried in that spot weren’t any better. It will be interesting to see what GM Jeff Luhnow does with these spot, as Gattis and Carter are both “his guys” - he’s now past the point of getting rid of the guys from the previous regime and now is going to have to decide whether he’s made the wrong call on Gattis/Carter/others. There are some in-house alternatives:
Jon Singleton, who’s had multiple brief shots in the majors but hasn’t produced; on the other hand, he’s only 23.
A. J. Reed, who is rated as the top first-base prospect in the minors; a typical high-power high-walks big slow guy who led the minor leagues in home runs. On the other hand, he hasn’t played above AA yet.
Tyler White, a low-round draft pick who has hit like crazy at every level, including .362 in half a season at AAA. Could be a Dave Magadan-type low-power no-field no-run guy who hits enough to make it worth it.
Or they could try to sign Chris Davis, or they could make some kind of trade.
Other than that, they might make a play for Craig Kimbrel as a top-end closer, or could potentially try to improve the top of the rotation with one of the top free-agent starters; it will be interesting to see how high the budget goes and what the GM chooses to do with it.