I don't know of any service that works exactly like Spaboom... with the "instant" build your own capability, and easy of use for the client. Also, it's a piece of cake for the business owner, it only costs you something if you've already made a sale...
There are other services used by big name retailers and service providers, such as
http://www.giftcertificates.com
http://www.givefun.com
http://www.giveanything.com/
These services are a bit different than the SpaBoom model as customers will receive a gift card in the mail, or an e-certificate. When they redeem it with you, you log in to the parent site, enter the information, and you will receive a perceneforum.xxxe of that sale in 2-4 weeks, usually in the neighborhood of 75%.
But... for the web-savvy, who are selling to clients who don't mind the shopping cart system, and waiting a day or two for their certificate to arrive in the mail, OR if you wish to also sell a few luxury goods, you might look into Google Checkout. They offer a service that is (while still in beta) looking to be as robust as Paypal webpayments Pro (which costs $20/month just to have,) if not more usable. They also have terrific rates- just 2% of transactions, and it deposits to your account, just like any merchant credit card processing account.
The only downside I can see (other than needing to know how to set this up,) is you cannot process phone orders yourself on your google checkout. Maybe there is a way, but I'm not seeing it.
Also, some forums report that payout (how the $ gets to your personal account from your google account,) can be very slow, up to a week +, and a few people have reported that they have not received payout at all. It appears that these issues are mostly related to inaccurate account information being supplied, which wouldn't be google's problem, but there are a few that sound like it's just a glitch in the system.