Try some of the sweet pimento varieties. They are generally very thick-walled.

Hi Bart,

Here's a few more you can look at:

hot - biker billy, manzano
med - chile de agua, chimayo, NuMex varieties
mild - anaheim

Rick

I'll second Denninmi's recommendation for pimento types. The largest I've grown was the heirloom "Greygo", which gets 4-5" across with very thick walls, and is completely sweet when ripe. "Tennessee Cheese" is smaller (3-4") but more prolific, and has a smokey flavor when ripe. I would define "smokey" as 'it doesn't taste hot, but don't rub your eyes after cutting it' (spoken from experience). Both are very thick walled peppers. I like using them in canned salsa because they don't turn to mush when chopped, and hold their shape well after cooking.