Patagonia Perla Negra Light is pretty unique. In fairly small quantities (2-5%) it comes across kind of pretzel-like, and can become too much in the 5-10% range (at least in non-black beers). It has a unique character for sure; it's kind of a "super toasty" malt without stepping into the roast department. Not much bitterness or astringency from it since it's huskless. Probably the closest thing I could compare it to would be pale chocolate, or pale choc mixed with amber malt. I have not tried the Medium or Dark varieties of Perla Negra.
Homemade torrified wheat can add a subtle toast quality to a beer in decent proportions (~10-15%) without becoming too much, and it's very easy to make in an air popper. Add about 1/2-3/4 cup to the popper, turn it on, wait for the kernels to pop, dump on cookie sheet to cool. Takes <1 minute per 4-6 oz.
Homemade torrified rye is in the same "super toast" ballpark as the perla negra above. It imparts a big toasty quality that's probably most similar to brown malt (plus popcorn). Make it the same way as torrified wheat but it takes about 3x as long (~3 minutes per batch) because the kernel just take that much time before the "pop". I'm sure the extra toastiness is due to the extra time.