Yeah your choices are lexspell (Free to use but has a registration nag screen if you dont pay) which I recommend, bbcorrector (Free but requires a setup), espell (costs money), or waiting for the guys at getempower.com to come out with their free spell checker...
I heard also that Rim was planning a software update to include a spellcheck on the 8800. The 8830 & 8300 already have this feature. I tried espell but it stopped working and have not started trouble shooting it.
I could be a bit off on this but I believe that 4.2.2 OS has a spell checker included (thus the 8820 and 8830 both have it already included as well as the curve and the pearls) but the 4.2.1 load does not which is what the 8800 users are stuck with. The latest version soon to be released is 4.3 as 4.2.2 is already out there on the included devices listed above. RIM released 4.2.2 to service providers long ago but the service providers have not made it available as an update to the 8800 users. It has been assumed that the reasoning is to encourage 8800 users to upgrade to the newer models. One of the bigger desires for many, over spell checking, is the newer media player on the 4.2.2 OS's and above. It's a nicer interface with full screen video capability.
One of the main reasons I keep an eye on the forums is to hear of a 4.2.2 release for the 8800. Who knows if it will ever happen but there's no technical reason not to according to RIM, just marketing on the providers behalf. I understand this and if placed in the position to make the decision I would likely do the same thing. But knowing this doesn't mean I have to like it!
This promise about the 8800 spell check was in the late 3rd quarter in 07 and what was heard then is the 8800 would get the spell check in the 4th quarter. No Joy Yet!
With the new lower prices on the 8310's and the fact that the 8310 is just a better platform overall, my guess is the same as some others here: They want everyone to upgrade!
The 8800 is still a nice phone but without the little extras like camera and built in spell check it just does not compare. And, with the 9k on the horizon with all the fun stuff the 8310 has, the 8800 will be retired to the same place the rest of the 7290's and 8700's are - In a box collecting dust...!