I've found that I have this problem too. I'm not a small guy - I have a 38 inch waist and weigh ~220 pounds - and I still have problems showing. Hell, sometimes I even show in jeans - so I buy those big (usually 44x30) and cinch them up with a belt.
There's nothing I can do about business clothes except buy big there too. I always buy off the rack then tailor - my favorite dress slacks are Claibornes (don't remember where I got them) that started out at a 44" waist. They have plenty of room up front, but I still get self-conscious every once in a while, when I just have this feeling like "Jesus Christ, you know everybody can tell - it's practically obscene."
The night I took my GF to prom (eons ago), afterwards I changed from my Dress Blues into a nice suit at a friend's house. She caught a glimpse while I was changing and said something about it. I couldn't come out of that room for an extra 20 minutes after I changed, I was so self conscious.
Sometimes though, you just have to suck it up and drive on, and realize that you are who you are, and people are going to look. I honestly don't know that very many people notice or even care.