Christmas means people will be looking for gift ideas for bassists who already have an instrument and an amp. Although effects are personal choices, do you have any idea for what might be a good first effect for the bassist who has s none? Chorus? Compressor? Wah? Overdrive? If so, post 'em here or do a formal review here: http://www.musicgearreview.com/review-entry-form.php

OK -- these are not effects, but I'll post two suggestions that are valuable additions to any player's gig bag:

Electronic tuner: Take your pick of many under $40, but if your bassist plays a five-string, make sure the tuner can handle a low B -- some can't.
Recommended: Korg GA-1 or GA 30 Guitar/Bass Around $20
If you have more money to spend and want a tuner that can be used onstage, consider the Boss TU-2 Chromatic Tuner and power supply. This tuner has a pedal that takes your signal offline for silent tuning via LEDs. It has the added benefit of acting as power supply for Boss effects. Street cost is about $100.

PlanetWaves Bass ProWinder peg winder: Makes changing strings easy. The winder accommodates "elephant ear" tuning pegs and includes a wire cutter for snipping off excess string length. Less than $10