I second human hybrid. Swapping a honda motor is pretty straitforward.
These engines will bolt in w/o any modifications:

-D15B2 Your stock motor.
1.5 16V SOHC PGM-FI 1493 92hp@6000rpm 89tq@4500rpm
'88-'91 Civic DX/LX (USDM)


-D16A6 a tiny bit of an upgrade....
1.6 16V SOHC PGM-FI 1590 108hp@6000rpm 100tq@5000rpm '88-'91 Civic Si
'88-'91 CRX Si

-D16A8/9 (aka DOHC ZC) A significant upgrade, but still no modding needed.
1.6 16V DOHC PGM-FI 1595 137hp@6800rpm 108tq@5700rpm
'88-'91 Civic/CRX Si (JDM)

Edit: There's also a SOHC ZC, but I don't have the statistics for it laying around. It may or may not be less expensive than the DOHC, pending on the dealer. A ZC will run you at least 400 with ~30-40k miles, whereas the d15b2 and d16a6 shouldn't run you more than 200. But the extra 30 hp does feel good