" ... I do, however, want you to have a list of your magic items! Up for grabs will be magic items levels 6 through 11. Also, available for purchase will be magic items levels 1 through 5. Whenever you are at camp you can purchase items, and in between levels, while you are leveling up, I will be populating the next level with magic items based on your preferences and your roleplaying."
So how do you pick a magic item? Do you pick it based on looks? Function? Damage? Hmmm... The first step to picking a good magic item is to have all available information. Thanks to Wiggi's website you should have access to most of the information you need. Start with the Player's Hanbook then go from there. Tons of items are in the Adventurer's Vault, and if you have a character from PH2 you may find items in there as well. Also, the splat books for the power sources like Martial Power have items specific to it. You can even find items in the Draconomicon and Open Grave. But you will have everything you need if you go no farther than the Player's Handbook and Adventurer's Vault.
The second step is to compliment your build. You'll notice themes in character developement. If you have a dude that does lots of damage, targets Fortitude and knocks people prone at 4th level, he'll be doing the same thing at 24th level. (Ignoring Don's whiny protests). So identify the one or two things your dude does well and amplify it. Imagine you had a Cobra. It goes fast. As you tweaked it over the years you do things to amplify it's strength: speed. You wouldn't, conversly, decide it needs more utility and add a flat bed or third row seating. A character is the same way. If your dude doesn't do a lot of damage adding the perfect magic weapon won't help that much. Figuire out what your dude does do and amplify that. You will be happier and the party will be more effective as a team.
The final step is to shore up your weaknesses. I know I'm contradicting my second point, but this is still valid as long it is a secondary objective of magic item selection. Upon occasion you create a character that does everything you want, but he has one tragic flaw that really chaps your hide. Remember Sleeper's dwarf? Sleeper had a ton of fun with him, but it really bugged him he was sooooo slow. One pair of magic boots later, problem solved. Again, this is shoring up one major weakness to improve your overall functioning and fun, not making your character flawless. A flawless character is generaly good at nothing. Using our Cobra example, imagine you had a Cobra in Texas and it was so hot you could hardly ever drive it. One air conditioner later, problem solved.
This is just the tip of the iceberg and I'm sure you guys have more insight than I. So let's hear it! What's your secret to optimal magic item selection?