Here are some very nice, small varactor diodes made by Siemens and others,
type BB-833, specifically optimized for up to 2.4 GHz applications (1 MHz to
2.4 GHz), tuning ratio is 8.6 (!) for voltage change from 1 to 28 Volts,
capacitance is 9.75 pF at 1 V and <1 pF at 10 VDC, to give you an idea of the
range. Looks like these would be fun for electrically tuneable filters and
certainly for oscillator applications. Small, surface mount package (the little
black specs on the orange label in the picture are diodes...). You get 12
pieces. Have fun!
Remember, I combine shipping to save you money, so ask for an invoice on
multiple item purchases before you pay!