Ok I was looking at direct investing in the bond market through my
broker, but wasn't 100% sure from all the advice that I have gathered
over time as to what kinds of bonds I should invest in, here is my
objective:

1) Maximum yield over 3 to 5 year time frame (I may want to cash out after 3 years)
2) No interest (coupon?) payments needed necessarily, rather it
maximize value over those 3 to 5 years
3) Credit risk important, think grade A- or better 

Suggestions? Advice?