Now contrary to popular belief you don't really need anything fancy to create some nice designs. A lot of my designs I'll use dotting tools or brushes that I bought from eBay in packs for a very cheap price.
Dotting tools:
I picked up this set of 5 for just £1.45 here and they've served me perfectly since! They're ideal for not only doing dots (who would've guessed?), but also other designs like hearts etc.
Brushes:
I also managed to find a great bargain on these at just £2.72 from eBay here and I've had absolutely no problems with any quality issues. This 15 pack comes with all you will need - striping brushes, smaller brushes and large fan brushes.
Other than those I really don't use a lot else for the designs. Some looks I have used things like studs or stickers in but again you can pick them up at less than £2 from various eBay sellers!