Just to echo the sentiments of a few here, it really isn't about money. It is more about the exposure you are able to generate for the company. If you are mixing it up at a decent level, playing good venues, getting good press and gigging frequently, you are in a good position to be approaching companies for endorsements. Obviously the chances vary from company to company and I do know that the economic downturn has affected the way that some companies are approaching their budget with respect to artist relations. 12 months ago, Warwick were asking me to go over to Germany to meet with them and now, despite the fact I can do way more for them in terms of getting their name about (not that they need it), they wouldn't be interested.
The final lil tip I can offer, is don't ever expect freebies. You will only get these if you are a big big name and it really is in the companies interests to be doing so. With all due respect, I doubt that you are a big enough name so the best you can hope for is discounts or trade prices.
If you have anything specific in mind, drop me a PM and I may be able to offer a bit more help