Oh, hell yeah! Have I got recommendations!
I do a review thread that has sunk quite badly because I haven't listened to any new audios since February. The scoring system is more than a bit skewed until I change scoring systems, and it's very much a case of Your Mileage May Vary, but it might help.
http://www.wrongplanet.net/postt220222.html
If you can afford it, I wholly recommend the Fourth Doctor Lost Stories boxset. The Foe from the Future and The Valley of Death are both good stories.
As for Seventh Doctor stories, there's more than a few I could recommend. Colditz is one of the better mainstream stories, and The Harvest is a good story that introduces a new companion called Hex, but one of my personal favourites is Night Thoughts. It's pretty horrific, but it's a damned good story. Just don't listen to it at night. Similar is the story Master, which is pretty cheap at the moment. And then, there's Unregenerate!, which, despite having the early Seventh Doctor and Mel, is a damned good story.
I could name a few others. You got Spare Parts, which is excellent. Here's some further suggestions...
Fifth Doctor
The Kingmaker
Sixth Doctor
...Ish (only available as download now)
Eighth Doctor
The Chimes of Midnight
Dalek story
Jubilee
Cyberman story
The Silver Turk
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(No longer a mod)
On sabbatical...