I watched a couple of videos on Totalbiscuit's channel recently of him (he's a terran player in gold) being coached by the caster dApollo of team Dignitas in the UK.
These are excellent for someone of my level. In particular there's a TvZ game, which is one of the two matches that I've been having real problems with. dApollo's advice to Totalbiscuit is to go mech for that matchup, on the basis that any sort of marine-tank build, as used by all the professional players, relies on excellent marine micro to avoid baneling splash damage. If your micro is not so good, mech is much easier. dApollo also said that the famous mech player Goody (who I really like watching) goes mech because his APM is low for a professional.
This has been a revelation for me, and I am now firmly a mech player TvZ. I have always had a problem with low APM, so changing my unit composition to something which stresses the things I am better at (strategy and macro) and places less emphasis on things I'm bad at (micro) really helps. I have tried mech TvZ four times and won three of those games against solid gold league zerg players - the sort of players who were steamrolling me when I was going marine tank. Mass blue flame hellions supported by siege tanks and thors is just awesome.
I am still working on a build order for this matchup - I've downloaded some of Goody's replays from www.sc2rep.com to try to find something I can copy. He has an early attack with 5 marines, three hellions and a medivac which he follows up with an uncloaked banshee and this seems to be absolutely devastating if done right.
The build order is your standard 2 gas 1-1-1:
12 Rax and make marines
@100 gas build factory
while factory is building take second gas
when factory completes make starport and start making hellions
when starport completes make a medivac
when medivac completes make a techlab, then a banshee, then rally the banshee to the zerg main
The medivac pops at about the time of the third hellion (ish), then you load up 5 marines and use the medivac to elevator the 5 marines and three hellions up the side of the zerg base. The goal is to kill the queen in the main and to do whatever damage you can before escaping. The zerg player may pull back the queen from the natural to the main, but then this second queen can be killed by the banshee, possibly leaving the zerg player with no anti air. You can then redrop any units you had left from the first hellion-marine attack.
I mucked it up the one time that I did it, but still took out one queen and a load of drones, and caused a massive overreaction into lings. I am quite excited to try it out again.
You can then transition into blue flame hellions, siege tanks and thors. The key I think is to get thors up asap in case he goes into mutalisks early on.