I rarely make a card without embellishments of one kind or another because I love the texture, dimension and coordination of color that they provide. It is next to impossible to choose just one...but, if I have to...I would say my favorite is Sticko Dimensional Stickers. They have a little dimension, come in a million shades and shapes, and don't add so much bulk to the cards that I have to put extra postage on them. (Here in the US, it costs 20 cents more if cards are too thick.) And because they are flexible, I don't have to put an extra piece of cardstock in the envelope to prevent the embellishment from tearing through the envelope.
Here are 2 of my favorite Totally Stampalicious! images with Stickos on them.
"Beer Guzzlin" Gus was colored with Copics. The designer paper is American Crafts "Celebration." Spellbinders Petite Ovals were used for the image and the words.
"Birthday Gus" was colored with Copics. Again, I used Spellbinders Petite Ovals and Scalloped Petite Ovals. The designer paper is from the "All Wound Up" Series by Daisy Bucket Designs. EK Success rick rack border punch was used to cover the seam between the papers.