I scoffed at cyclists in those tight black britches for a long time.
Then I bought some when I became a regular 10+ mile per day bicycle commuter. I make no claims that these are the best or anything, but they're perfectly adequate and happen to be the ones I have: http://www.performancebike.com/webap...47_-1___000000
I don't bother when I'm just riding around with my kids or running (oops, riding) to a nearby store or something, but for anything, say five miles or more, I wouldn't go without them.
I think the wicking sweat function is just as important as the padding. They'll keep you cooler and drier than wearing regular underwear under street clothes, jeans, cargo shorts, etc. Beware if riding trails with trees branches and such. They are thin and tear easily. Sometimes I wear cargo shorts over them if I need to carry pockets full of stuff, and I have one pair with a small hole on an outside seam that I will only wear under other shorts for that reason.
I have seen the padded underwear (like the REI briefs mentioned above) but they seem to cost nearly as much as regular cycling shorts, or at least the relatively inexpensive ones I linked above. I figure you can wear cycling shorts alone or as underwear, effectively, so why limit yourself to underwear-only for nearly the same cost?
In warm weather, I also wear inexpensive, bright-colored wicking tee shirts from places like Wal-Mart and Target. Example: http://www.hanes.com/shop/hanes/men/...170621180107:s