Just a quick disclosure: I generally like clear, rubbery cases. I tend to always gravitate towards a brand name cases like Spigen or Otter Cases. My normal preference as of lately has often been a Spigen Crystal Shell but sadly, you won't find much love for the HTC Bolt (in terms of case options).
The good news is, you will find plenty of generic aftermarket cases and my experiences have been pretty good overall.
I chose a case made by Tauri; "HTC Bolt Case, Tauri [Scratch Resistant] Slim Thin Clear Flexible Soft TPU Protective Case Cover for HTC Bolt - Clear ", which was the closest thing I could find to a Spigen Crystal Shell. It's very bubbly, but has a good grip. All the port holes are in the right places. The fit is nice and has a good grip overall. I think the current cost is $7.99 on Amazon.
I've had it on the phone for over a couple weeks where I use pretty heavy. It sets the heat off a little bit, adds a good bumper around the parameter of the phone and it pretty much up to spec with other phone cases. The clear color has remained pretty clear (even with the heat) and no yellowing from what I can see (which is a good sign).
At this point, it has survived as a good short term case (will keep on long term) and will let you know if anything changes. Hey, at $7.99 it's not much of a gamble so if you like what you read, I'd give it a try.
-Rob Ignatowicz
Sprint Product Ambassador
Disclaimer: The Product Ambassadors are Sprint employees from many different parts of the company that love technology. They volunteer to test out all sorts of Sprint devices and offer opinions freely to the Community. Each Product Ambassador shares their own opinions of these devices, therefore the information in this post does not necessarily reflect the opinions of Sprint. The PA's do not represent the company in an official way, and should not be expected to respond to Community members in an official capacity. #sprintemployee.