Well, if you liked the "main" storyline of Btech(Warrrior Trilogy, Blood of Kerensky, Natural Selection, Assumption of Risk and Bred for War) then the next set to read would probably be the Twilight of the Clans series starting with Exodus Road. Once that series is done, then there are the tie in's to the FedCom Civil War series starting with Patriot's and Tyrants.
Of course, if you did not like the "main" storyline, then Sigma's suggestion of Wolf Packor Close Quarters are as good a choices as any though I have not read either myself.