Congratulations on getting a house and/or your wedding
Unfortunately with the current interest rate environment, you cannot expect a very high return given the short-to-medium term period of 3-4 years.
On one end of safety, we have fixed deposits. The highest in town should be ICICI HiSave's
1.7% pa for a 3-year FD. Maybank's board rate is 1.2% pa for a 3-year FD. Alternatively, if you are not comfortable with that long a term, ICICI or CIMB have 1-year FDs at 1.1% pa. 1.7% pa means a total return of about $1,020 on your $20k. This is the baseline.
I wouldn't go into stocks, even high yield stocks, because who knows where the market will be in just a few years' time. The ideal would be a bond or single-premium policy that matures in 3-4 years that gives a somewhat higher return than plain FDs, but there haven't been many such offers for retail investors recently.
I like one of the bank preference shares listed on SGX, OCC 3.93%. Provided OCBC chooses to redeem on the earliest possible date in Mar 2015, the return is around
3% pa at the current price minus brokerage. There is minimal credit risk but some term risk in case OCBC chooses not to redeem and you have to sell it in the open market. However, this issue can be illiquid - there were no trades today.