One modification I did early on to the Sportster was adding a new pair of shocks. I opted for a pair of almost new Road King shocks. They were a little longer than my stock factory shocks and I rode it that way for awhile. But later I added a pair of lowering blocks from Tamarak (great products by the way).
You need longer mounting bolts and a number of washers to space the shocks to clear the belt guard and struct covers. I bought my shocks for $50 and a Harley plumbing kit for the local dealer. Pretty basic and easy to do and is probably one of the better low cost modifications especially when riding two up.
Pictures are before the lowering blocks.