Here is a system that requires a small bankroll and uses a very small progression, but has been profitable on early tests. (Riverbelle Wheel)
It involves betting on high/low, even money bets (3 double streets, 1-18 or 19-36) on Live Wheel. (I haven't tested it on an RNG, so Live Wheel only.)
Step 1.
Before making any bets, track for 20 spins the frequency of hits of high/low.
If high has more hits, your progression will favor high. If low has the most, progression will favor low.
Step 2.
Wait for 3 spins high/low to miss in a row and begin betting. (I start with $1.50, @0.50 for low/high double streets)
If win, wait for next 3 spins high/low to miss.
If lose, (remember, watch the total high/low hits). If high (or low) has fewer total hits (from the 20 spins earlier) don't bet. (wait 3 spins high/low to miss)
If high/low has the most hits (from the 20 spins) Bet again 2x. (Final progression.) If miss, wait for next 3 spins high/low to miss and begin at original bet.
(Bankroll suggestion: no more than 10% of 2x bet.--i.e. $1.5/1st--$3.0/2nd bet**$30 BR)