Lots of people would think the best way to support a race or racing in general is to sponsor things.  Hand out cash for King/Queen of the mountain, primes in crits (does anyone do primes at crits anyway?!), donate cash to add to prizemoney pools and so on.

I think that's sub-optimal.  I think the best way to support racing is to get involved in organising, promoting and competing in races.  I personally don't know anyone that cares terribly much about how much prizemoney there is for a race.  I won a moderately big handicap way back in my enduro days (Lenny Hammond H'cap 2004) and it paid $250 for the win.  Not bad, but to be honest, if it was $10 or $500, it wouldn't have made any difference to me and I didn't even consider prizemoney when I entered.  The win was the thing and Mal Sawford's writeup in Cycling News and the CCCC website was the crown jewels. 

Most of the people I race with and work with don't care about prizemoney.  They like bling prizes though, but using bling prizes to effect is the key.  The way CCCC use an aggregate for their crit series, for example, is fantastic.  Riders from every grade have a chance (although with CCCC's crits, realistically it's won by A grade riders most of the time but that's because they promote grades on wins and winners trickle up until they stop winning) and it encourages regular participation.  Aggregates, rewards for outstanding performances and the like are good, I think, and our experience at the Summer Sprint Series seems to hold that to be true.  The few A grade lads that win most of the races most of the time don't make the field, it's a quality field across the grades that makes for great racing for everyone and I think prizes and event structures should reflect that. 

At the SSS we scaled our aggregate performances by grade and while an A grader did win the overall, daily aggregate prizes were split across each grade and in '07-'08 the aggregate was tied between an A grader and a C->B grader and it was decided by fractions of a second in the end, so really, everyone did have a chance.  I reckon we've stumbled onto a good model that allows riders at any level to have a chance at the 'big' prizes, without us as organisers spending loads of cash. If I give you $50, you pop it in your wallet and spend it on who knows what, it gets lost in general revenue and forgotten .. but if you win some 'thing', it's a better prize, I think and if you have a chance to win the same prize as the top riders, then grading really does work.

Back to supporting ... The best thing riders can do is to hype the events they want to happen.  If you want a quality field to race in, YOU have to help get people there.  That means talking up events with your riding chums etc.  Just showing up on the day to race is not enough.