As people are sticking their heads over the parapet with the advice giving, maybe I could put in a word or two?
Firstly, I see a lot of advice about keeping profiles short & light-hearted, not 'giving too much away'. I'm afraid that I disagree: I think the best profiles give a genuine flavour of you ... mine do and whilst I don't get much in the way of mail, I do get second dates ... in fact, many of my second dates morph into short-term relationships. Thing is - I'm over 50, I'm fat, I have short grey hair & I'm not pretty (yes, of course I have qualities but this isn't about me or my self-esteem). The point is that I'm not an easy sell and the people who talk to me do so because they find me attractive and/or interesting ... rather than some bland or sanitised version of me. They are drawn to what they see in my profile and as I'm pretty much what I say on the tin (and my photos are accurate & recent - I also advocate complete honesty about the basics of height, body type, age etc), its tends to go well. Yes, I've been involved with a couple of men who were less than hunks, but the last one was 6'4, broad shouldered and head-turningly good looking. So, showcase the real you in your profile is my first bit of advice. BTW, I love what watch has suggested for sponge - particularly the idea of opening with those contradictions that make sponge unique.
Secondly, the paying sites. Yes, they're expensive, but they do have a better quality of members (generally). For example, I've never seen any of the hun 'n babe brigade on the Times, Telegraph or Guardian. There are very few players as why bother to pay to play when you can get playtime for free. There are even fewer scammers but I'm sure we're all wise to the warnings signs there and can easily step over them. The sites I've mentioned all allow you to put up a profile, browse profiles, 'favourite' or 'like' members, as well as read any messages you've been sent. You have to pay to message anything other than a selection of one-liners. Personally I recommend something called London Dating which is fronted by Time Out but puts your profile into the databases of the Times, the Telegraph as well as Time Out itself. If you join up and do nothing for a while (perhaps don't load a photo, write only the bare minimum), the site will get around to offering you a discount on membership at which time you can give it you full attention. You can also record a voice message either to support your online profile, or to be put into Time Out's listings - but you may get a more ooooo errrrr response to those (or perhaps I'm just lucky that way!) The membership deal is competitive when compared to the Guardian who are monsterously expensive. My two longest online dating relationships came via this site but I'd also chuck in a word for Love & Friends. It is a bit London/SE-centric though and is not as good as it once was. There are far too many wonderful women on there so the men can really pick & choose. You can use it in a limited way for free but the membership rates are lower than most of the pay sites.
Of course the two people I'm currently talking to are both from OKCupid but there's nothing wrong with spreading yourself about a bit is there ...