As much as it is fun and probably the right thing to do to have kids make their own super hero accessories, sometimes there is a pressing need to play with a certain laser beam that can't be satisfied by any glue and paper in the world.
Hence, a few toys that any self respecting little kid hero wanna be seems to absolutely need (says the mother of a 5 year old Batman/Spiderman/Ironman/Zorro/Sometimes-Darth-Vader-Because-Bad-Guys-Are-Cool):
1. The Super Why Letter Game ($13.10, Kmart)
2. Design Your Own Superhero Cape Kit ($39.99, Magic Beans)
3. Spiderman FX Gloves ($16.99, Toys R Us)
4. Batman Raincoat ($48.99, SimplySuperHeroes.com)
5. Iron Man Cardboard Stand up to protect the bedroom ($35.99 SuperHeroStuff.com)
6. Superhero Capes with Masks ($25, HandmadeHaley on Etsy)
7. Thor's hammer ($20, Gensquared on Etsy)
8. Captain America's Shield ($8.49, Amazon)
9. Thor's Helmet ($8.74, Amazon)
10. Iron Man Gloves ($9.99, Target)
(images as linked above)

Ercol Bar Stool
I got a pretty awesome knit batman mask on etsy
When our baby was born, my cousin got her and my five-year-old son matching super hero costumes as a new baby/big brother gift. I dare you to find something cuter!
Your son sounds like mine! I don't think I've seen them in stores lately, but over the summer my son got a Superman and a Batman t-shirt, WITH CAPES at Target for $8!! Every time he wears them he thinks he's awesome, and so does every single person we see. I mean, just constant compliments from strangers. He gets a big kick out of it. I know you can find them online, but they cost more. I'd say it's probably still worth it though. If you're shopping for a little boy and you come across a superhero shirt with a cape that he can wear any time? Buy it!
I also made him an awesome felt hulk mask which he loves, I copied one off etsy and it was so easy and cost about $1.25.
Anyway, this is a great list. My son has or is getting some of these same things and some very similar. I think that's the same sheild he has, he loves it. I wouldn't waste twice the money on the one that throws discs, unless the kid specifically wants that one. But his shield, hammer, masks, capes, figures, etc. are played with daily. He's getting the web slinger for Christmas, slinging webs is his favorite superpower.
lyndsay.j.becker - We have those shirts with capes too! Baby gap is currently selling a bunch of them as well. My 4 year old gets the biggest kick out of them. We also have all the super hero masks, like the Thor helmet, which are easy to store and provide hours of entertainment for my super hero obsessed boys.