For startups, Google[1], Amazon[2], Microsoft BizSpark[3], OVH Digital Launch Pad[4], Digital Ocean[5], have startup programs that you can apply to with varying amounts of service credit (usually expiring afer one year). (Don't write off OVH: theirs seems to be the smallest, but their stuff is by far the highest value.. 2GB instances for $3.49/month and great DDoS protection; however, their cloud dashboard takes a little time to get used to, but seems pretty powerful once into it.)
1. $20k to $100k in service credits @ Google: https://cloud.google.com/developers/startups/
2. $5k at Amazon, $15k in accelerators: https://aws.amazon.com/activate/
3. Up to $120k at Microsoft: https://bizspark.microsoft.com/
4. $500 to $100k at OVH: https://www.ovh.com/us/dlp/
5. up to $100k at Digital Ocean (not sure if this is actually launched yet -- we applied for https://userify.com but never heard back): https://www.digitalocean.com/hatch/