Certain Cryptocurrency and Fiat Exchanges have referral programs, and each have unique rewards.

Altcoin

• Decentralized exchange (DEX)
• Refer 10 people - Earn 5% of trading fees from your referrals
• Refer 25 people - Earn 10% of trading fees from your referrals
• Refer 50 people - Earn 15% of trading fees from your referrals
• Refer 100 people - Earn 20% of trading fees from your referrals
• Refer 500 people - Earn 25% of trading fees from your referrals

Binance

• No. 1 Ranked Cryptocurrency Exchange
• 20% Commission of referral trading fees
• Unlimited referrals

BitShares

• Decentralized Exchange (DEX)
• Has a Lifetime Membership Program (Current cost is 111 BTS, roughly $30/USD)
• At it's core, the Network takes a 20% cut and the referrer takes a 80% cut of transactions fees. There is also a way to modify that so the referral can get a set % refunded.

BTCpop

• Cryptocurrency Exchange
• PoS (Staking) Pool
• BTC Loans
• Earn 0.5% Commission on ALL referred repaid loans UNDER ฿5.0
• Earn 0.25% Commission on ALL referred repaid loans OVER ฿5.0

Coinbase

• Cryptocurrency/Fiat Exchange
• Very user friendly
• Once your referral(s) buys/sells $100 worth, you each get $10 in BTC

CoinExchange

• Cryptocurrency Exchange
• Maker Fee Commission: 2.50%
• Taker Fee Commission: 5.00%

Crypterium

• Cryptocurrency bank
• Referrals get 1% rewards and will be added to your referral program
• You get 5.0% of all CRPT tokens purchased by your referrals

Cryptopia

• Cryptocurrency Exchange
• 10% of referral's fees converted into DOT

HitBTC

• Cryptocurrency Exchange
• 75% commission from users you have referred
• Create as many referral links as you want

Robinhood

• Stock trading App/Cryptocurrency Exchange App
• Has ZERO trading fees
• The referrer and referral each get a free stock, ie. Apple, Sprint, Ford, Microsoft
• Can get a maximum of $500 worth of free stocks

StakeUnited

• Online staking pool
• You get 10% from the fees of each stake

Upcoin

• Cryptocurrency Exchange (Trading opens March 1st 2018)
• Will be adding Fiat capabilities later in 2018
• Has a 4 tiered reward system (Each % represents a number of all referral fees generated)
  • 'Newbie' 0% reward
  • 'Partner' 20% reward (Need 10 activations)
  • 'Premium Partner' 30% reward (Need 30 activations)
  • 'VIP Partner' 50% reward (Need 50 activations)

Yobit

• Cryptocurrency Exchange
• Receive 20% of commission for every trade your referral makes

I know I didn't list all of them, feel free to comment ones you know of and use. Thank you!