Legitimate work-at-home jobs do exist, but “it can be really hard to find real openings with all the scams and bogus business opportunities out there,” notes Sara Sutton Fell, CEO of FlexJobs. A team of researchers at the site have checked out their work-at-home job listings to make sure they are on the level before they post them.

FlexJobs reports a 25% increase in mobile or work-at-home jobs in 2013, mostly because technology has made it practical to do more kinds of work remotely. “We’re still surprised by some of the positions we come across,” says research director Kelly Kirby — including senior analyst, nursing case manager, account executive, accountant, software developer, webmaster, and virtual teacher.

Some of the companies using technology to hire and train people over greater distances, she adds, are big names in their industries, like Apple (AAPL), Xerox (XRX), UnitedHealth Group (UNH), Dell, ADP (ADP), and American Express (AXP).

Each year, FlexJobs publishes a list of the 100 employers who posted the most work-at-home and remote jobs in the preceding 12 months. The top 25 on the current list:

1. Xerox
2. UnitedHealth Group
3. Dell
4. Aetna
5. American Express
6. First Data
7. Humana
8. Westat
9. K12
10. ADP
11. Overland Solutions
12. CyberCoders
13. U.S. Department of Transportation
14. SAP
15. PayJunction
16. Connections Academy
17. Apple
18. IBM
19. HD Supply
20. Salesforce.com
21. Western Governors University
22. CACI International
23. About.com
24. McKesson Corp.
25. Aon

Job hunters who aren’t looking to telecommute right now, but think they might be someday, can use Flexjobs’ list to check out which companies already seem most receptive to the idea, Sutton Fell adds. “It can be helpful to know which employers to keep an eye on.”